Put a white king and a white knight on an empty board against a black king and you can shuffle for a hundred moves without ever attacking anything worth attacking. There is no mating position to aim at. Not a hard one, not a long one: none at all.
That is why king and knight against king is drawn the instant the last pawn disappears. Under the FIDE laws it is a dead position, so the arbiter stops the game whatever the clocks say, and it is also why you cannot lose that ending on time. If your flag falls and your opponent has only a knight left, the result is a draw.
Give the knight some company and it mates anything
A knight is the best mating piece in chess in the right position, because it jumps. No pawn wall, no rook, no line of defenders stops it, and a king that has castled behind three healthy pawns is exactly the king a knight likes.
8 
7 
6 
b That picture has a name, the smothered mate, and it turns up in real games far more often than you would guess, usually at the end of a queen sacrifice on g8. Notice what makes it work: every square around the black king is occupied by a black piece, and the knight attacks from a square nothing can reach. The white king is on b1 doing absolutely nothing, which is the difference between this and every basic mate on the list.
Keep a pawn, or keep the half point
Two practical things.
If you are grinding out a win and the position is heading for king and knight against king, you have to keep a pawn. Trading down into that ending throws away the point no matter how well you played the first forty moves, and I have watched a junior do it with two minutes on the clock and a winning position.
If you are the one defending, count what your opponent has left. A lone knight is a draw. A knight and a pawn is not, because the pawn can promote, and then you are facing a queen with king support.
The same logic applies to a lone bishop, and to two knights, which can mate but cannot force it. If you want the knight’s good side instead, spend twenty minutes on smothered mate puzzles and you will start seeing Nf7 in your own games within a week.