If you have the flush at the flop, I believe the chance someone else among 8 opponents was dealt the Ace-high flush hand in that suit is:
16/47 * 8/46 = 5.92%
The first number is the chance the Ace is among the 16 cards dealt to your opponents. The Ace is 1/47 but we dealt 16 cards, i.e. 16 chances for that card to have come out. The second number is the chance that player has another card in that suit given he has the Ace (8 of that suit remaining).
Note that this is only the chance the hand was dealt, not that the player is still in the hand. The chance someone folded Ax preflop will vary. And no, the rank of your cards is irrelevant, we only care that you don't have the Ace.
And if you hit the flush on a later street than the flop, just adjust the unknowns in the denominator accordingly.
For your other question, I think you meant if you have KK what is the chance someone else has AA, but it's the same answer.
For that type of problem you can do an approximation that is very close. Given your hand, there are 1225 other possible starting hands your opponents can hold, from C(50,2). And there are 6 ways to make AA. So the chance a player does not have AA is 1 - (6/1225). And to approximate the chance one of 8 opponents does have it:
1 - (1 - (6/1225)^8 = 3.9%
This is a very close approximation, because if we scale the exact 10 player answer from http://people.math.sfu.ca/~alspach/mag88/
4.39% * 8/9 = 3.9%.