Everybody has something to say about colleagues and talking about them can help get students talking about more personal things, which can really help them exit their comfort zones. A few good questions could be:
What do you think about your colleagues?
What are some common problems with colleagues?
Have you ever had any challenging situations/altercations with your colleagues?
Do you spend time with your colleagues outside of work? Why/why not?
Who is your favorite colleague? Why?