Well for one thing, I know who's not a skrull, and that is Jean Grey since she died as Jean Grey did not revert back to true Skrull form and was reborn as Jean Grey during End Song, thank the gods, lol.

I would kinda hope that Emma has been, that would explain her desire to be a good girl and infiltrate the X-Men like she has, and it would SERIOUSLY mess up Cyclops, he's probably look like Apu when he found out his wife had octuplets, lol, sorry Simpson's joke there, ha ha.

Spider-man would be another, what nerd in his right mind would ever give up the one woman who loved him enough to marry him, lol, ask Bill Gates.

Xavier would be nice too but since he died when he was shot then he wouldn't be a skrully either.  Scarlet Witch would be awesome considering that horrible M Day fiasco, but I doubt that any Skrull could possible harness that kind of power.