Sometimes you may have the makings of a discovery but lack anything good for the knight to do when it unmasks the other piece; you would like to give check but aren't within range, and the knight has no obvious threats to make against other pieces either. Remember, then, another idea: look at the enemy king; see its vulnerabilities, and any pieces you have bearing down on its position. Sometimes adding the knight to those other pieces can create a threat of mate or other serious trouble that can anchor a discovered attack as effectively as a check. The point can be put more generally. You already know it is important to look for checks and to create ways to give them. It also is important to watch for—and create—mating threats, as they often serve similar purposes just as well and are easier to devise. Just aiming a piece at a square next to the enemy king may be enough to create a useful mating threat a move later when you aim a second piece at the same square—and aim it at a loose enemy piece at the same time.
In this first position, White has a classic arrangement for a discovered attack: his knight masks his fianchettoed bishop, which otherwise could take the loose Black bishop on b7. But what threat can White make with his knight that will keep Black busy? The knight seems far from any targets, and certainly can’t give check from where it now sits. The key is to examine Black’s king and notice that White’s queen already is aimed at a square next to it: h7. If White plays Ng5 his knight adds more pressure to h7, and now White is a move from mate with Qxh7. (The simple pattern of a knight on g5 supporting a mate threat by a queen aimed at h7 is familiar and should be absorbed.) So Ng5 is as effective as a check; Black is equally required to pause to fend off the threat. He will do it with QxN, of course. That then leaves White to play BxB. Is the trade of pieces a wash? No, because Black’s rook is stuck on a8, and will be taken by White on his next move.