Dramatic Irony is when the audience or reader knows more about something than a character. In this scene, Macbeth and Lady Macbeth are discussing killing Duncan.
A good example in Act 2 is that Duncan is going to be killed, but he doesn’t know it! Banquo and Macbeth’s conversation is another example, because Banquo does not realize that Macbeth is plotting his death.
Finally, Act 2 Scene 2 contains dramatic irony as well. Macbeth and Lady Macbeth are running around furiously, trying to cover up Duncan’s murder. The audience knows that they are imagining things because of their guilt and fear, but they think that there are supernatural messages all around them.
Me thought I heard a voice cry “Sleep no more!
Macbeth doth Murder sleep”—the innocent sleep, (Act 2, Scene 2, enotes etext p. 30)
Macbeth is concerned because he could not say “amen” and Lady Macbeth is frustrated and running scared because Macbeth is talking crazy talk.
Who was it that thus cried? Why, worthy
You do unbend your noble strength, to think
So brainsickly of things. (Act 2, Scene 2, enotes etext p. 30)
Both of them hear the knocking and get frustrated by it. Lady Macbeth comments that it will be easy to wipe the blood off her hands, foreshadowing her later descent into madness as well.
As was mentioned in the previous post, dramatic irony is when the audience is aware of something that the characters in the play are not. In Act Two, Scene 2, Macbeth has just murdered King Duncan and becomes hysterical while he talks to his wife. Throughout the conversation, Macbeth mentions that he heard one of the chamberlains cry "Murder!" while the other said, "Sleep no more! Macbeth does murder sleep" (2.2.35-36). Lady Macbeth is confused, and her husband continues to insist that the chamberlains were crying "Sleep no more!". When Lady Macbeth leaves to place the bloody daggers by the chamberlains, Macbeth begins to hear the sound of knocking. After Lady Macbeth comes back, she also hears random knocking. Both characters believe they hear noises and Macbeth is certain that the chamberlains were aware of his actions in their sleep. However, the audience is aware that these noises and "supernatural occurrences" are simply a figment of their imaginations which makes this scene a good example of dramatic irony.