If I transfer a character to Argent Dawn or The Scryers; will I still be able to play with friends on Shadow Council and Laughing Skull?
You can play with anyone from any North American realm. You will want to make sure they are a battle.net friend, and you’ll have to put them in your group.
Because The Scryers is an American roleplaying realm, you may see people from Shadow Council when out in the current expansion content by random chance due to cross realm shenanigans.
Is Argent Dawn an European realm? If so, you would not be able to play with characters on Shadow Council and Laughing Skull from there.