This may be what you're looking for ..or it may help....I don't know.... a lot of people get confused over this (including my wife and her partner who just
can't seem to get it.

..)
nb - I should note people have ALL sorts of leading conventions, and theories. I'm just listing what I think most consider "standard" at least by American standards....
1
Suit contracts. In the USA for generations, the standard lead (opening lead and otherwise) from AK was the King. Of course, from KQ that was also true. So, on opening lead, 3rd hand was unsure what to do if he held the
Jack.
If opening leader holds KQTx or KQxx, then encouragement is good! But if opening leader has led from AKTx, then 3rd hand knows that declarer's got the Queen, and you don't want him to continue! omg ... what to do??
Thus, many good USA players now on opening lead at suit contract, lead
Ace from AK, and (as always) King from KQ. This disambiguates opener's holding for third hand. (Of course you trade off and get another ambiguity in return, but that's more tolerable, so the adherents of this procedure hold).
However, A from AK is a trick-one agreement only. For other than the opening lead, continue to use the "standard" (in US anyhow) method of leading the King from both AK and KQ.
2.
NT contracts. If you've decided to lead a suit that contains AK, and if you've also decided to lead one of the big ones (rather than e.g. fourth best), lead the King.
Leading the Ace at NT on opening lead (provided you're not leading partner's suit or some other exceptional circumstance applies) asks third hand to unblock == to throw away the K, Q, or J if he has one of those, or else to give count.
(NB - Giving count is very popular and is better, but old-timers may still always play their
highest card, even if it's a non-facecard-honor, so you need to clear that up with your partners).
This helps opening leader when he has a long suit that he wants to run.
n1: should this procedure apply at trick 2 and thereafter? To discuss with your partners.
n2: a lot of people reverse the A-K meanings here, and use "Ace for Attitude, King for Count"
n3: there's no substitute for common sense... you still have to think about it when partner opens with the Ace at NT. Could something else be up?