knight's mat

I have looked at several chess theory books, but have not found an answer to the question: Is it possible to checkmate two knights and a king against one king? I am a very beginner myself and have not found an answer through experience.

If your opponent is stupid and climbs into the corner with his king, it is possible to checkmate with 2 knights. Generally, it is a draw if you dance around the middle of the board for 50 moves.

but give some examples of such a position, e.g. white: R e3 and f3 K g3 and black: K f1 or something like that

It's impossible to win.

If the opponent helps, then it is possible to win.