The players that receive the training are those that play minutes at the position listed in training during games that week (excluding private league and BBM). To receive full training they need to play 48 minutes or more if age 20+ or 45 minutes or more if 18-19. So no, he would not receive any training if he plays PF and not C.
You can switch to 2 position training (PF/C) although the amount of training received is a little less than one position only.
Think of the position listed for each player as a suggested position. It has no in game or training impact although it does matter for salary calculations.