My good friend who is married is constantly asking me how one of my girlfriends is doing. I wouldn't think much of it if it was once in a while but it happens every time I see him; He wants to know how she is doing and what she has been up to. One time I noticed his wife give him a sharp look because he brought her up. I know its just a harmless question but I was wondering if it sounded like he might have a crush on my friend? I'm not going to bring it up to him its just something that I've noticed. Curious what others might think?

It kind of does sound like maybe he's got his eye on her. Most deffinetly if his own wife gave him a sharp look over it.
I would talk to him about this, for it might become a very big problem.

Married people have crushes all the time, some harmless that keep the marriage alive, and some home wrecking, and there's no way we can tell at a distance, nor do I think even close friends should start speculating. Let it be, unless asked to be involved by them.

Here is what you do. The next time he asks tell him your not comfortable talking to him about your friend and suggest he either stop asking you or contact her himself so long as his wife agrees.