What is Corin or Afton of the Volturri talents?
All members of the Volturi guard have some sort of talent. However, it was never made clear exactly what Corin and Afton's talents were. The Volturi are "collectors" of sorts. They only care to have in their circle, those who have special gifts or talents. Jane, for example can manipulate the minds of others to think they are writing in pain. Marcus can track anyone who he has had even the smallest mental interaction with. The Volturi desperately wanted Alice and Edward to join their coven (they were of course refused). Knowing all of this, it would be okay to infer that any "helper" of the Volturi's possesses a gift. Perhaps this is something that we will discover in books to come?
Both Corin and Afton are apart of the Volturi's Guard rather than the Volturi Coven, who are the Aros, Caius, and Marcus. And the Volturi guard is usually full of vampires that have gifts except for Felix. I've heard that Corin's special power would be the ability to paralyze any vampire just by biting them which has a great move when in vampire to vampire combat. I don't think Afton's ( as well as others) gifts were mentioned.
Corin has paralytic venom, which probably means his venom can paralyze a person. As for Afton...well, I'm searching myself...if I find the answer I will respond again =)