The complement of the Being a good mentor question.

I work with many very senior people that have vast amounts of knowledge and wisdom in Software, Engineering and our business domain.

What are some tips for gaining as much knowledge from them? I don't want to take up too much of their time, but also want to take full advantage of this since it really could help develop my skills.

What are some good questions to get the conversation rolling in a sit down mentor/mentee session? Some of the people providing mentorship have little experience in this area, so it would help to be able to lead some of these discussions.