I'm sure that there have been many threads on this before and a search should bring them up.
Some questions I recall asking and advise our medical students to ask include the following:
1. What is the general composition of the residency classes (gender distribution, FMG's, etc.).
2. Which facilities do you rotate through and which facilities are considered "home base".
3. How many hours do you work on average and what is the call schedule like.
4. How many months of in house call do you do and what happens when you are post call.
5. Do you have a pre-op clinic where interns do most of the groundwork for you.
6. Do you have CRNA's.
7. Do you compete with CRNA's for cases.
8. What type of support system does the department have built in for family needs, personal tragedies, etc.
9. Do residents easily achieve their numbers.
10. Do you farm out residents to meet your numbers.
11. What type of fellowships are available.
12. Do the graduating residents get the fellowships they want.
13. What is the board pass rate and rank of the current classes compared to the rest of the nation.
14. How are the didactics set up.
15. When do you start getting to do the difficult cases.
16. Has the program been on probation recently.
17. Has there been a large turnover in the faculty.
Those are just a few off the top of my head.