r/AskHistorians has an excellent book list that may be of interest to you.

In particular it recommends 3 books on Holocaust denial: Denying the Holocaust: The Growing Assault on Truth and Memory and History on Trial: My Day in Court with David Irving., both by Deborah Lipstadt, and Lying About Hitler: History, Holocaust, and the David Irving Trial by Richard J. Evans. These three books discuss the history of Holocaust denial, and debunk many of the common myths and misconceptions promoted by deniers. As you can tell by the titles, the latter two centre around the Irving v Penguin Books case, in which David Irving sued Lipstadt and Penguin Books for libel after Lipstadt called Irving a Holocaust denier in Denying the Holocaust. The books, and the case itself, offers a fascinating insight into the way deniers try to obscure and bend the historical facts, and the way historians evaluate historical evidence.

In the mean time, you may be interested in checking out the FAQ on the Holocaust, and on Holocaust denial. It is a very common topic on this sub, and a previous answer may be of use to you.

(Edit - updated links).