Hi, hopefully one of the WWII/Holocaust/Holocaust Denial experts will drop by with more specifics for you, but fyi there have been several lengthy posts on denialism. I took a browse for some recent ones that can get you started:

• Monday Methods: Holocaust Denial and how to combat it featuring /u/commiespaceinvader

• How plausible is it that the Holocaust never happened? - OP seeks confirmation of denialist claims; /u/commiespaceinvader provides a take-down

• Holocaust questions OP is a denialist seeking a platform; again taken down by /u/commiespaceinvader. Post-thread discussion here Sunday Digest | Interesting & Overlooked Posts | September 19, 2016–September 25, 2016

• Are there any misconceptions the public have about the Holocaust, that might be hard to explain without coming across as a Holocaust denier/revisionist?

• What Can One Say to Holocaust Deniers?

• background: When and how did Holocaust denialism start?

• you may also find the conversation between /u/commiespaceinvader and /u/kieslowskifan of interest in this thread: Good points to raise with Holocaust deniers?

Several of these posts have been archived by now, so if you have follow-up questions, just ask them here & tag the relevant user's username to notify them