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.
My SO got annoyed with me one day, because I was chuckling so much reading this book. I couldn’t explain why it was funny (I mean, you should just read it), so she couldn’t laugh with me. I cannot read this book around her.