There's a website that allows you to search what books/readings are assigned in college courses.
https://www.opensyllabus.org/
The most assigned "Holocaust" related books appear to be these (I've added the popularity score the site uses in parentheses)
1) Viktor Frankl, Man's Search for Meaning (86)
2) Primo Levi, Survival at Auschwitz (77)
3) Hannah Arendt, Eichmann In Jerusalem (77)
4) Christopher Browning, Ordinary Men (74)
And then a bit further down,
5) Art Spiegelman, Maus (64)
6) Elie Wiesel, Night (62)
7) Zygmunt Bauman, Modernity and the Holocaust (56)
From there, it seems things drop off a lot. Anne Frank I'm sure is the overall most read, but it seems to be less commonly assigned in college (scores only 17), probably because it's often assigned in middle school.
I'm surprised Browning is so high, though Ordinary Men is the most "human interest" focused of his books and so in that way it fits somewhat with the more typical memoirs and novels. Arendt's book, an essay collection, is probably the one most unlike the others.
I had not heard of the Bauman book. It's from 1989 and argues that contrary to the "conventional wisdom," the Holocaust was not a lapse into barbarism but rather distinctively "modern." Idk, it seems to me that idea was present in the earliest Holocaust propaganda. The "industrial" or assembly line mass murder, etc.
For upper level elective courses, it seems you might see authors like Longerich or Friedlander. Or if a broader Third Reich focus, maybe Kershaw and Evans. It looks like there are a variety of books assigned with moderate frequency on "genocide" more generally.
Bloodlands by Timothy Snyder scores a 40. So somewhat popular. It's in part about the Holocaust but it tries to integrate this with Soviet mass killing in the same territory.