Each chapter in the book ends with an interview question followed by the analysis of what an interviewer would look for in an answer. Write one of these yourself.
Besides my love for learning random techical factoids, this question is really getting at how well can someone teach something. It's good for the topic to be a little obscure so I can see how well the candidate gives context or answers questions.
Another angle here is learning if someone digs into things they're curious about.
If someone gets stuck on this question, I would suggest some things that I've learned or ask follow up qestions about projects that they've worked on in the past. Hopefully, one of those will shake loose some tidbit of knowledge.