Our modus operandi is to look for double attacks with the knight and ask whether they can be made to work. This time you're playing the White pieces. Notice first here that your knight is on a dark square; now look for Black pieces also on dark squares. You find the Black rook and king, and ask whether they can be forked. They can, with Nd5+. Now ask: Is d5 protected? Yes, by the pawn at c6. But before worrying further you examine the pawn to see if it is constrained. It is; it’s pinned to the king by the White rook at a6. So Nd5+ is safe, and it forks and wins the Black rook. This position is structurally about the same as the previous one.