If you mean fully trained, this is how you check. (assuming you're playing Generation 4)
1. Grow lots of EV berries (26 of each will be enough, but it works with less)
2. Save the game
3. Feed EV berries to the Pokemon you want to check and count how many of each it ate before its stats stopped falling
4. Soft reset or reboot
The number of berries that lower its stats is EVs/10 rounded up. For example, if your definition of fully EV trained is 252 Atk/4 Def/252 Spe, then it will lose EVs from 0 pomeg berries, 26 kelpsy berries, 1 qualot berry, 0 hondew berries, 0 grepa berries, and 26 tamato berries.