Not including short story collections, poetry collections, anthologies, etc.
For me, I believe it’s Oroonoko by Aphra Behn because it was on the syllabus for three different classes that I took in college. Other than that, the most I’ve read a single book is twice, and that was Telegraph Avenue by Michael Chabon. I’ve read Dracula 1.5 times. Didn’t finish it the second time around.
I’m also not in the habit of re-reading even my most beloved books. But I have made some exceptions: #1 of re-read novels is hands down: War and Peace. About 20 years ago, I was in the habit of reading it every Christmas season (not sure why - other than it’d generally be the longest continuous span of time I’d have free). Probably read it 5 times in that era. Before and since then have read it at least 2-3 more times. Last read was 2 years ago; so I’m likely going back to it soon. Second to that, in my younger years, I’d have to guess it would be either The Hobbit, Dune or the Chronicles of Narnia. Lastly, I’ve read One Hundred Years of Solitude, Anna Karenina & Great Gatsby at least 3x each.