whats the average dmi of a player here?
You'll find that DMI isn't necessarily the best way of judging how good a player is, as it relies a great deal on the player's form, listed under "Practice this week".
does the training counts for all the players or only for the ones in your team that played a game?
Training counts for any player that has played at the position being trained. For maximum effect, you want your player being trained to have played in one full game, or 48 minutes, of game time.
should i look at the positions the players have to put a player on another spot? like when i have a point gaurd that has the best stats to play on shooting guard?
You may find that one of your point guards would play better as a shooting guard than any of your shooting guards. The player's "best position" is a guideline, and there's no inherent penalty in playing someone out of their "best position".