did Eddie Coyle know he was getting waxed?

I'm not sure. I mean, he was very cagey about what he said, for fear that those he acquired guns for would think he betrayed them. That's why you hear Detective Foley complain to him that the information Eddie gave him was too late to be of any use. In turn, Eddie was careful about what he divulged, trying to play it down the middle.

I'm thinking, but I don't recall a moment in the film where it was made clear to him that he knew he was thought of as a rat. Obviously, he knew he'd fit the profile since he made it clear he didn't want to do any ( more ) time, but I don't think he knew they knew.

That last night at the game at Dillon's invite I think it was Eddie thinking "what the hell...I may as well at least have a fun evening to forget about the mess I'm in, even though it's temporary". I really don't think he would've taken up Dillon's invite if he knew he was going to be murdered, even if he was mellowed out from alcohol and having a good time.

I believe Eddie thought this was a sort of going away party for his prison stint. After all, these were his "friends". Eddie was playing checkers in a world of chess.