Anybody on your team who got minutes last week got training, not just the guys who popped. Whether or not you see an arrow next to a skill, they still got training. How fast they pop depends on how many minutes each guy got (48+ gets you full training, less than 48 gets you some smaller percentage of training), how old the player is (the younger they are, the faster they train), and how many positions you trained, among other things. The fewer positions you train, the faster guys will pop. So if you do single position training, you'll get more pops than two position training, which will get more pops than team training. Don't be discouraged - no pop (no arrow up) doesn't mean no training.
To train a PG at inside shot, you'd have to play him out of position (as SF/PF/C) that week and then train that position. To train driving, you train one on one, which is for guards, forwards, or team.
Hope that helps!