I haven't played it yet.But I want to know cause I've planed out a team.
P.S. If it's late in the game.Then where is GTS?
You do it the same way as Black and White: the PokeTransfer. You do it after beating the game.
GTS for Diamond: Jubilife City.
Black / White / Black 2 / White 2: 2nd floor on any Pokemon Center except the Pokemon League.