Do pokemon always gain the evs they need most by battling themselves?

Question

EG. Starly gets a speed ev from starly.

Answer 1

The EVs a pokemon give off reflect what type of moves they typically use. For instance, Gengar, a pokemon commonly used for sweeping, gives 3 special attack EVs when defeated. Battling the same pokemon you're training won't give you any extra benefit. The easiest way is to battle the ones with the highest EV yield, which can be seen here.