Question

"What does Macbeth imagine he sees as he waits for the signal from Lady Macbeth telling him that the guards are asleep"

Answer 1

During act 2, scene 1, when Macbeth is waiting for the signal from Lady Macbeth, he hallucinates and sees a bloody dagger floating in front of him.

This vision is interpreted as Macbeth's guilt for the murder he is about to commit. The dagger he sees is the same weapon he is about to use to kill the king.