Whether a character comes from Dawnport or Rookgaard and arrives in Mainland then rooks themselves they always return to Dawnport. However, I do know in Dawnport if you speak to the NPC Inigo by saying "Hi, Rookgaard, Yes, Yes" he can send characters up to level 9 to Rookgaard, but only ones which are not the first character on a new account. (Source) This is what the NPC told me when I asked him if I could go to Rookgaard a second time: "Inigo: I'm sorry, but I cannot let you go there, you'll get much better training here than on that ancient isle." Please note, you might have to log in and out in order to speak to Ingio to go to Rookgaard. The reason I might've had trouble is that I asked him to take me to Rookgaard already today on the new character so this will be my second time arriving there. Or maybe there is just some sort of glitch. So just know if you have trouble try logging in and out. In case you're interested I made a list of what you lose and don't lose when you rook yourself.