Welcome to the Forum Emlyn (and to the game).
You click on the player's Skills, round up his Quality (Q) to the next 5 and mutliply by 3. Subtract the 3 avgs at the bottom then divide by 0.2.

You see my picture 2 posts up (the one with the red triangle shirt)?
His Q is 29, so round up to 30. x3 = 90.
Subtract 27.6, 31.4, 29.4 => 90 - 27.6 - 31.4 - 29.4 = 1.6... divide by 0.2 => 8
So 8pts until the next star
Now go to Training and look at the player's Progress bar, this shows you how close he is to the next point.
Also next to it is Gain: how much increase in % from the last training session or match