It's hard to say exactly without knowing the rest of the hand. Does East have reason to guess that South has the ace? What does West's lead of the 8 mean? Where in the hand are we? What is the contract? NT or trump suit, and is this trump or not?
Either way, W probably isn't underleading A8x. Even if there were no other suit to play, there's just no reason not to play A. So E knows A is in South most likely; there's no reason for E to play the K there. But, E also might have only two - 5 is a weird choice otherwise. Why play 5 from K52 or K54? It's not like E wants to encourage...
On the other hand, W really shouldn't underlead Kxx or Kxxx. No matter the contract, it's probably a bad lead. It's possible W has no choice - if this is the only suit left, for example - but if this is early and W likely has a choice, it makes more sense for E to have the K based on this lead. It's just unclear why W led the suit in the first place.
You also may want to see their carding agreement - 8 from 842 is a reasonable lead in some agreements, it's not in others. Would they lead 8 from 82? 2 from 842? It's possible you can eliminate some holdings from the lead of the 8, but again this depends on their card.
As far as the play of the 6 goes, Declarer is announcing that they have the T by not covering, so they should cover with the 9. There's just no reason not to, not even transportation-related reasons. Put the 9 on and see if that draws out the K. It might, might not, who knows, but you can always cover with the T anyway if you prefer to be in hand.