I'm training my 6'9" 18 y/o MVP. He's got good overall skills (all average/respectable) except JR (was atrocious, now pitiful after 1 week). I will train OS wingmen all season and maybe some next season. That should reveal what other skills get trained.
Interestingly enough, I'm training my 23yo 6'7" MVP
(4487875) After 3 weeks of training, with 4 full trainees and 2 partial trainees, I've had pops in only JR and JS (and not very many pops, I can assure you).