I don't really know how you accomplish that.
I get that many students don't care about history class. I mean it wasn't even my favorite (well there were multiple history classes throughout the years, but just in general). But even as a complete footnote and total not giving a shit, how does one not know what the Holocaust was? I mean I don't need specifics and names of concentration camps. A simple "Nazis hated Jews and killed plenty of them during WW2" is more than sufficient.
Fuck, you don't even need school. You bump into this stuff by accident if you are at least a slightly curious human being. The odd movie here and there, some random news article showing up on your news feed, random story of great great grandpa in WW2, Anne Frank being brought up for the billionth time cause your kid is learning about her in school or you bumped into some hipsters listening to Neutral Milk Hotel or it was on Good Morning America that it's some random anniversary of her birthday. Like what the fuck? You pretty much learn about the Holocaust by accident frankly if you live in North America or Europe even if you don't give the slightest shit about something that happened 70 years ago. Shit you even know about it if you listen to the deniers for fuck sake