Go out with him; coffee, dinner, something that can easily put him in a socially dominant role. Does he offer to pay, order for you, go to the ticket counter for both of you. These things can just be him being polite, it could also show a sense of what he is like deep down.

A 'dom' has a hard time turning it off. I do little things throughout my day that half my friends, and all my sub friends, have mentioned. Ultimately, if you walk behind him does he lead?

You are a sub and you know it. Show him a small part of that and just guage how he responds.