Is it possible that there are some, who don know the holocaust happened?
Yes, I fear. There is a growing movement to either decry the Holocaust completely or minimize it. Some are the white supremacists who simply refuse to believe that it occurred. Some are people who cannot handle the FACTS about what occurred. I am certain that the vast majority of people, at least in America, know the word and concept of “Holocaust”, however, they refuse to acknowledge that it was real. I am certain that had Germany been able to hide it, they would have. However, they were literally caught in the act. Japan DID manage to hide their war atrocities and came out smelling like a rose. Very few know of Unit 731, the rape of Nanking, etc. The only reason we know about the Holocaust is that Germany did not have the chance to wipe it from the history books. Edit: I see that I answered this twice. I must have been sleepy.
Of course, there are. Worse is that there are people who know but won’t say that they know. Some of these stay at the entrace of Auchwitz and other crematoriums and tell everyone they can that “it never happened.” So many probably do not know: children born since 1950’s who live in “third world countries” and others born elsewhere in the world whose children and schools have not told or taught them. Adults of those days are nearing death these days and while they may all remember in Europe, Japan and China, I don’t believe that all of such adults in the world even at that time took note of it even though there were newspaper stories, movie news, television, speakers, books, and more that told about the horror of the holocaust.