There's someone in Opelucid City that can check your EVs (in Drayden's house, or at least that's what it is in B2W2), but just like Bianca in B2W2, she'll say something vague, e.g. "You Chandelure put great effort in speed!" or something along those lines.
If you've only been training speed, then 252 is the max a Pokemon will take in a stat anyway. If that's the case, just keep training speed until you know you've hit 252.