You can check here:
Your Pokemon need to be at LV 50 or 100. If you want to check for your Pokemon's IVs, you need to know its exact EVs to do so. You can also check if your Pokemon has high IVs In-Game by going to the Battle Subway. Also, you can check to see if your Pokemon's EVs are maxed out by going to a house in Opelucid City.