Here Black does not have the kernel of a discovered attack; the point of the position is that when you see a configuration like this—bishop and rook coordinated, with both trained on squares near the king—it pays to experiment with creating the pattern for a discovery by bringing one piece into the path of the other and examining the consequences. Here an obvious way would be Rc2+: the rook moves into the bishop’s path and gives check; White’s king has to move. If it goes anywhere but d1, it leaves the knight loose and Black takes it with his rook on the next move. (Always ask whether an opponent’s forced move would leave anything loose.) If White moves the king to d1 to protect the knight, he completes the pattern for a discovered check by putting it on the same diagonal as Black’s bishop. Now Black would think about what he could do with his rook in two moves. Don’t obsess over the knight. Think broadly about the opportunities created by a discovered check; look for any White piece Black could attack with his rook in two moves. Rc7+ would unmask check by Black’s bishop, and attack—and then win —White’s rook on h7.