The answer is Nh5, with a nice rook check to follow. The idea seems to be to reach a R+2p vs N+p endgame.
But what if we start with the rook check then play Nh5? Black has several options such as letting White queen and winning the rook, but it seems to me White still has an advantage after queening and capturing the g pawn - reaching a Q+N+2p vs. Q+N endgame.
Starting with a rook check is a mistake! W does not win any more as Black now can play 1...Kc5=.
Also, 1...Ke7 2.Nh5 would not win for White either, as due to the black King move Black can now play 2...Qb8!=