Iirc karkat knew slick was his exile or at least a carapacian he interacted with would be his exile, was it ever explained how?

I can’t quite recall him acknowledging Slick as his Exile, however, consider this: Slick is the polar opposite of the word ‘subtle’, and the moment a Player enters the Session, they’re open to having the Exiles chat them up through the Station Terminals. The first thing we see Slick say to Karkat post-Intermission is like, “Been a long time”. Between that and I bet the THOUSAND times he told Karkat “Just stab that fucking thing, come on”, anyone would be able to determine who that voice in their head is.