[fecak]

I think you find out what makes them happy in their job, and then try to provide that as best as you can. Saying you are "happy doing what I'm doing" is based on the present state.

You could ask "what do you like about what you are currently doing?", or "is there anything you think that could make you happier?" (this question can have unintended consequences, as "more money" is a likely answer).