It doesn't matter if the player is listed as PG or C. If you choose 1 position training for centers the players who played as centers during the week will get the training (proportionally to the minutes played as center).
Just 2 reminders: 1) training is updated every friday, so what counts is the training regimen set when training is updated on friday; 2) players should get 48+ minutes in the position trained in order to receive maximum training.