Here are a few of the questions that I like to ask:
- Tell me about a time that you influenced the product direction.
- How do you define the role of product marketing?
- What is the one thing that we can help you with, that you can take away from working here?
I also agree with Carrie that case studies are the best. I like to ask about a specific project from the resume and then go into great deal about that particular experience. I look for self-awareness and ability for the individual to describe success in terms of results as well as acknowledge learnings and areas to improve.