Can you fork a knight?

Yes.

Yeah sorry I just wanted to ask for a knight forking a knight and I kinda forgot about other pieces

You can if the knight is pinned to the king then certainly can you fork the knight to the king if it is in the right place

Discovered Check

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I wondered if that was what you meant. Technically no, since theoretically the knight could capture the forking knight. But as @ShouryChess1234 pointed out, IF the knight being forked was also pinned, then yes. Consider also this famous position:

Black to move and win?

The winning move here is...Nd4! This wins at least a Queen for 2 minor pieces, because if Nxd4, Black has Qh2# Thus, Black is forking the Queen and knight. The f3 knight can move, but it wouldn't want to, and of course if the Queen moves, Black follows up with Nxf3+ and Qh2#

Α knight can fork a knight too- taking the forking knight can be either bad, or impossible (if the forked knight is pinned).

Is it a fork after Nf6+, or not?

we are talking about a knight forking a knight we all know that pawns can fork knight

no,the king can't.

Pawns are often effective at forking knights because knights usually have to move around the board in a way that makes them vulnerable to pawns advancing and attacking them.

Please stop--my head hurts!

Yes. There are many, many ways to both fork with a knight, and also fork a knight. Or in your scenario, fork two knights.

In other words, a knight can be both a forkee and a forker. And it can even be both at the same time.