Unfortunately, this whole process is a huge game.
Showing that you know about a program, and trying to find out the real answers to questions, usually results in projecting deficiencies in the program.
This is an uncomfortable situation for any interviewer to be in.. and it makes themselves see themselves in a negative light.. which means they think you do as well, which conversely results in them deciding that you're probably not interested.
I would only ask questions that you know the answers to, that project positive spins on the program, and in addition, enhance their perspective of your interest.
You should also cater those questions towards whomever is interviewing you.. ie ask peds questions to a guy who is a peds ortho.. not to the joints guy. You want whomever is there to do as much talking as possible. People love to talk and feel wanted, it's really all about the psychology..and getting a good conversation in.
Of course, there are always the generic backups which can be helpful in a pinch:
What new additions / changes are you expecting in the program over the next 5 years?
What type of research opportunities are there available (be careful with community programs. I asked this question at georgetown and was told if I want to do research.. look elsewhere.)
From your perspective as a <insert type of attending> what is the best feature of the program?
What made you decide to practice in this program?
What fellowships do people typically go for coming from this program?
What sort of case variety do you have in your speciality. Sometimes they love taht one because they can talk about it.
Don't fall into the common pitfalls questions of:
What's the case volume?
What's the interaction between the residents and attendings?
Is this program trauma heavy?
Is this an academic program?
What deficiencies does your program have?
There was a recent change in X with your progam, wassup with that??
....
Hope that all helps!