Firstly, everyone is different, you can always ask *him* if there's anything you can do to help 1-on-1 at some point. Although onto more general advice, the best thing would be to remain patient and attentive. One thing I notice coworkers doing whilst I stutter is looking like they'd rather be *anywhere else but talking to me*, which always feels shitty. So don't do that. I would also say don't avoid him, treat him like you would a normal person. No one likes being a leper, even if we know people are only trying to help. It's good that you're asking and that you care, you're a good egg :)