it doesn't work in wi fi, he just has sketch when the game is over, and I tried in battle maison... same result... x & y btw
The easiest way to teach Smeargle moves is to participate in a Double battle in which you use Smeargle and another Pokemon knowing the desired moves. Let your other Pokemon use the move you want to Sketch, then let Smeargle use Sketch on your own Pokemon. Then win the battle, learn Smeargle Sketch again, repeat.
A good way to get in a Double battle is to challenge the restaurants in Luminose City where you can choose what sort of battle you want to participate in.