"Tell me about a good book you've read recently."
There are a group of questions that interviewers use that are sometimes misconstrued by the applicant. The "good book" question is one of those. In a case like this the faculty member is trying to get a sense of your outside interests. It's a chance for the interviewer to see you as an engaged and interesting person. Misguided responses might be, "I'm reading a neuroscience textbook" to prove your intellectualism or "I don't have a chance to read for pleasure because I work so hard." Remember that having a compelling and kind demeanor is a large part of being a good physician.