Now to the matter of spotting knight forks in particular. You may be used to certain forking patterns: your opponent’s king and rook are a square apart on his back rank, inviting you to fork them. But it takes more care never to overlook a potential fork when the board is crowded and the pieces to be forked are not lined up so neatly on the same row. Consider the opportunities here for Black’s knight on b7. By moving to c5 it can fork four White pieces (find them); by moving to d6 it can fork two pieces. Whether either of these forks "work" is another question (the squares the knights need are guarded, though Black has possible replies, etc.), but don't worry about that now. It's just an exercise in geometry: we want to see everyplace where two White pieces are in a forkable position. Seeing only the obvious forking candidates is no good, and won’t lead to tactical magic. If they are obvious your opponent can see them, too, and can avoid them. You want to see all of the possibilities every time they exist.
Notice an important feature of the knight's movements: every time a knight moves it lands on a different colored square. This can be used to make your searching more efficient. It means that two pieces can be forked by a knight only if they are on squares of the same color; it means that they only can be forked by a knight that lands on a square of the opposite color; and it therefore means that if a knight is in position to deliver a fork on its next move, the knight and its targets must all then be sitting on squares of the same color. This is a valuable idea; consider it a law of knight forks.
To state the practical implication plainly, one way to build your ability to see all the potential knight forks on the board is to look for any two pieces of your opponent’s that are on squares of the same color as the square where your knight sits. If, as in this case, your knight is on a light square, scan the board for pieces of your opponent’s also on light squares. Can any two of them be forked by your knight? This only takes a moment; you aren’t yet analyzing whether any of the forks would work, but just are reviewing the board visually for simple patterns—a color scan. Sometimes this will be a helpful way to alert yourself to forking opportunities; in other positions it will be more efficient just to look directly at your knight moves without reference to square color. Experiment.