You did not say he is your friend and for that matter, I was wondering if said co-worker was female until your last big paragraph, so I'll assume its a he.I was just informed that a co-worker was involved in a crash this weekend.
For me, two things pop up, how much of a friend is he (how well do you know him), and is he gregarious, the type to talk about personal travails? If a buddy or the type who likes to gab (and listen) take him out for a beer or sit with him at lunch and break the ice by talking about your riding. You should be able to figure out quickly if he wants to talk about the accident or if he would be receptive to an invitation to take a refresher mc course (@Weaselinsuit's approach is brilliant).
As @Obo said, asking is caring, and also flattering. Just let his interest in discussing it (or not) lead you.
I'm obviously not of the camp that says ignore it until he brings it up. We are all bike riders, we (well many of us) wave at each other, and some of us even stop to help other bikers parked by the side of the road. Go for it!