No offense, but if you're still only an slp student you probably have a long way to go before you understand stuttering. I say this knowing a lot of slps, even ones with a focus on stuttering who don't know anything. They'll teach fluency techniques and easy onsets and diaphragmatic breathing and for the majority it doesn't do jack. It actually hurts because it mechanises speech and makes it programmed. But when you are in a tough situation it suddenly fails. I think the most helpful thing you can do is have him feel comfortable talking to you about his frustrations. That is how you're going to learn about stuttering too. It's a very unique disorder and unlike other speech disorders that have more of a prototypical treatment plan. But seriously, as an slp student, you can probably empathize with him easier than others and just having someone to talk to who has some impression of what's going on is probably going to help him than any techniques you could suggest.