I first asked this question on Stack Overflow, but it turns out this is a better place for it.
Imagine you were working as a software developer. Imagine that the manager of your team leaves and your company is looking for a replacement. Imagine that as part of the hiring process you had the opportunity to talk with him. You are not the only person doing an interview, and while it is not ultimately your decision whether or not to hire him, you do have an influence. What questions would you ask? What would you talk with him about?