First and foremost he needs to get 48 minutes on the position you train that week. If you train pressure, he needs to make 48 minutes on PG. How you achieve that depends on your team and goals. Most people try to set the player as starter, backup and reserve while having no other active players besides 4 other starters and at most 4 backups. This way the trainee usually makes 48 minutes in 1 game.
You can train the same skill multiple times in a row or alternate between different skills, it's up to you. There's some influence of the elastic effect, so I wouldn't endlessly train 1 skill, but otherwise it doesn't make any significant difference if you train X for 3 weeks and then Y for 3 weeks or wether you alternate each weeks. I usually let it depend on my league schedule on where I need to play my trainee (for example if I train a SG with low passing and a tough schedule, I rather train Jump Range that week so he can play SG and I play my veteran PG on PG to lead the offense).