I'm not sure if this is the right place to ask, but where do holocaust deniers generally think all the Jewish people who died during the holocaust actually disappeared to?

This question is a bit difficult to answer.

On the one hand, while Holocaust Deniers share the political desire to rehabilitate Nazism and spread anti-Semitic conspiracy theories, they are a historically varied movement with different waves and sometimes different arguments. While in the Anglo- and continental contexts of Holocaust denial we can observe a certain "canon" of supposed arguments emerge, certain strands of denial that emerged in the Middle East in the context of the Israeli-Palestinian conflict, while heavily borrowing from European and American deniers, can be viewed as its own specific tradition for example. For an answer on early Holocaust denial, see my post here

On the other hand, an almost universal method of Holocaust deniers, especially the "new generation" that emerged in the 70s, is more obfuscation and sowing doubt with lies than giving concrete answers. By dressing their lies in gown that is supposed to look "scientific" in their inquiry – their famed ~~numbers magic~~ – they aim at presenting themselves as serious scholars who call established findings into doubt rather than come all out as people screaming "Jewish World conspiracy!!!!" and "Hitler did nothing wrong!". With the pretense of scholarly conduct comes legitimacy and through that paired with their constant harping about there supposedly being "two sides of the debate" (which there aren't) they can succeed in spreading their deceitful and hateful lies. The explicit aim of which is to normalize their position in whatever society they find themselves in. The tactic, they reckon and count on, is to do that so once it is normalized to have "doubts", it will be easier to bring out the big guns a la "Jewish World Conspiracy", the racism, anti-Semitism and further hateful agenda.

In terms of the number of victims, several strategies employed by a variety of deniers have been employed:

Some are not particularly sophisticated in their arguments such as Walter Sanning a.k.a Wilhelm Niederreiter, a German with neo-Nazi leanings, who is staunch in his claim that all the Jews that were killed during the Holocaust and thus were simply not there anymore after the war, were in the Soviet Union. According to him they simply emigrated there or were spirited off there by the "Judeo-Bolsheviks". How they managed that under war time conditions in a country that imposed travel restrictions on its own citizens and regarded foreigners with great suspicion is anyone's guess except good Walter's I suppose but that is his particular approach. And he is not the only one, there is a couple more out there who say they just moved to Palestine/Israel. Which also represents some difficulty given Israel's population in 1948 but it's not like actual facts ever stopped deniers.

Others go a bit of a different route. Ernst Zündel, German emigre in Canada, for example simply denies that any Jews were killed at all and that in fact, the number of Jews in Europe grew rather than shrank during the war. His supposed "evidence" are numbers form the 1946 world almanac, which are alleged to show that the Jewish population after the war was the same as before the war. That the world almanac of 1946 explicitly wrote that they indeed did publish the numbers from 1939 in 1946 because no population count had been done in Europe during the war, does – like other proven facts – again not stop Zündel from writing this BS.

But by far the most common strategy among deniers is to do some weird ~~numbers magic~~ that based on falsified demographics or some other BS is intended to sow doubt about the death toll of the Holocaust or about the number of Jews living in Europe altogether. They prefer to point to alleged inconsistencies and small corrections made over the years to blow them up in an argument by insinuation that calls into question the existence of the Holocaust itself. In short, rather than answer the question you posed above, they aim to show that one detail is wrong and that by extension calls into question the whole historical consensus, no matter how firmly that is based in fact.

Take, for example, this thread where /u/Georgy_K_Zhukov and I engage these sorts of arguments. Here, the person tries to argue that based on actuary tables – a tool used by insurances to calculate the potential life span of a given individual at a certain point in time – the number of Holocaust survivors indicates that the estimates of the death toll of the Holocaust by historians is wrong. Now, they don't specify which actuary tables since those are a reflection of a specific point in time (life expectation having risen over the second half of the twentieth century) and applying them wrong since they are used to calculate forward and not backward. If applied backwards in the same manner as they are in the example thread, the population of Europe now, based on the population of Europe in 1945, would be a whopping 2.230 million instead of the 740 million it had in 2010. ~~Numbers Magic~~!

Another good example of denier tactics that floats around the internet like a turd on water, is what I discuss in this thread. By pointing to old newspaper clippings decrying the treatment of Jews in Tsarist Russia and mentioning the number of 6 million, they argue that because these articles describe 6 million Jews as in peril, the death toll of the Holocaust can't be true. How one logically follows the other is beyond me and should beyond any person willing to use their brain but that's them brakes when it comes to deniers. What they overlook is that the estimated total number of Jews in the pale of settlement in Tsarist Russia is about 6 million; a majority of whom but not all were later killed by the Nazis.

There are several variations of this ~~numbers magic~~ and demographic crunching but tackling them all would take all day and a whole book. What can be said about all of them is that they are based not on investigation and fact but on lies and distortion, another pertinent example of which I discuss in this thread in connection with David Irving.

In short, where Holocaust deniers address your question, they do so with ludicrous arguments. But for the most part, they don't and rather rely on putting evidence together that has nothing to do with each other, lying and distortion. Holocaust Deniers' modus operandi is to use arguments based on half-truths, falsification of the historical record, and innuendo to misrepresent the historical record and sow doubt among their audience. They resort to fabricating evidence, the use of pseudo-academic argumentation, cherry-picking of sources, outrageous and not supported interpretation of sources, and emotional claims of far-reaching conspiracy masterminded by Jews.

For more about Holocaust Denial, see:

Denying History: Who Says the Holocaust Never Happened and Why Do They Say It? by Michael Shermer and Alex Grobman (2002).
Denying the Holocaust: The Growing Assault on Truth and Memory by Deborah Lipstadt (1994).
History on Trial: My Day in Court with David Irving. by Deborah Lipstadt (2005).
Lying About Hitler: History, Holocaust, and the David Irving Trial by Richard J. Evans (2002).
Brigitte Bailer-Galanda, Wolfgang Benz, Wolfgang Neugebauer (ed.): Die Auschwitzleugner. ‚Revisionistische‘ Geschichtslüge und historische Wahrheit. Berlin 1997.

Holocaust Denial represents a wilful distortion or dismissal of fact for ideological reasons, so the list of answers to this question is particularly endless. Without wishing to fall too far down the rabbit hole, Deborah Lipstadt's peerless introduction to the subject, Denying the Holocaust, identifies a number of interconnected positions during the evolution of Holocaust denial, a number of which are directly relevant to your question. (Others, such as "It did happened, but Hitler didn't know" aren't)

As a caveat: Please don't take this to mean there are organised schools of thought on the matter, there really aren't. Holocaust deniers with entertain any contradictory nonsense so long as it services their primary agenda of either a) promoting antisemitism by pointing to a Jewish deceit and/or (depending on the political position of the denier) conspiracy, or b) redeeming Hitler, the Third Reich, the SS, the Wehrmacht, or the local collaborationist/puppet regime they most closely identify with.

One position is that Jews did die in large numbers during World War II, but this wasn't due to organised extermination - it was just war and terrible things happen during war. Common canards offered in defence of "deaths = yes/genocide = no" are either that mass deaths were caused by typhus or starvation thanks to Allied bombing campaigns (which neatly shifts blame too), or that Jews represented a fifth column actively working to undermine the Reich and so were lawfully targeted in reprisals.

The earliest pseudo-academic deniers posited that the Holocaust did happen, but the scale was exaggerated as a propaganda exercise to - depending on era - justify US entry into the war (note: the Holocaust wasn't widely reported in the US press, with a few distinguished exceptions), justify Allied war crimes, or to justify reparations to Israel.

In order to anchor this claim the number of Jews in Europe has to be argued downward. One tack is to claim that Jews successfully emigrated from Germany, originally to the United States but increasingly this belief shifted to Israel across the 1950s and 1960s. One of the ways this rationale is achieved is by noting the number of Jews who successfully fled Germany and Austria, but ignoring the fact that they fled to the likes of France and the Netherlands.