Is he not that guy’s boss? Who sets the agenda and who implements it?
I don’t know either way. Just speculating like the rest of us are.
Totally separate.
Head athletic trainers mostly exist to help players deal with the day to day, nagging injuries, rest/recovery, etc. 99% of the time they deal with stuff like ice, heat, cold baths, overseeing band resistance stretching and other kinds of physical therapy as players work back from injury, initial diagnosis of injuries, assisting players through other personal medical conditions they have to play through, stitches/quick repairs/resetting dislocations, etc. Basically a paramedic during games, and a physical therapy/rehab/spa with office hours the rest of the time.
For anything more serious than that, which requires a much more thorough diagnosis, there is a team doctor or the work is outsourced to a third party care system with the trainer being involved in the player's recovery from the procedure, not the actual procedure.
Trainers have absolutely nothing to do with players' workouts and training regimens during the season where there is a separate Strength & Conditioning coach (or in the case of the Rangers a slew of them) who manage workouts.
Not a knock on you (certainly not, since you're actually asking the question) but for the posters assuming he has anything to do with strength & conditioning - this is pretty standard stuff going all the way back to NCAA and even top flight high school hockey programs. About the only involvement the head athletic trainer would have in a player's workouts is whether or not to clear them to participate or use certain parts of their body.