At first glance, this question doesn't seem directly relevant to your job (unless you're in publishing), But look under the surface and this answer can be really valuable to an employer in figuring out what type of person you are and what type of employee you would make. Do you never read? This could signal to the employer that you're not intellectually curious or may send off red flags about workaholism (which can be a good thing or bad thing depending on the job).
Points to Emphasize
You might not be expecting this question so you have to be prepared to think fast. But also remember that this is a "fun" question where there is really no wrong answer, as you don't choose to talk about a book that is inappropriate or would cause you to be viewed in an unflattering light.
- If you haven't read a book in awhile, don't panic. If there is a book you can talk about intelligently and with enthusiasm, talk about that one, even if it's been awhile since you read it.
- If you don't read books very often, you could mention a highbrow magazine or newspaper that you read regularly, with the explanation that you tend to spend your time catching up on current events.
- This isn't typically a critical question so keep your answer brief.
- If you read widely, perhaps choose a book that's fairly well known on the chance that the interviewer has also read it and it will spark a conversation.