What are some major examples of irony in Act Two (scenes three or four, preferably) of Shakespeare's Julius Caesar?
Act Two of Shakespeare's Julius Caesar is thick with irony as the title character meets with some of the men who will participate in his assassination.
In 2.2, when Caesar urges some of the men to "Be near me", the audience knows that they will be near him, but not in the way that Caesar expects; they will be nearby to help kill him. Twice in that same scene Caesar addresses Trebonius and Brutus as "friends", not realizing that they are in fact his enemies.
In 2.3, Artemidorus reads a letter he has written warning Caesar about various conspirators. At the end of this brief scene, Artemidorus comments, "If thou read this, O Caesar, thou mayest live." The audience will realize that Caesar never does read Artemidorus' letter since Caesar is assassinated.
In 2.4, Portia thinks that her husband Brutus has some "suit / That Caesar will not grant" and she hopes that her husband will be successful in his "enterprise". The audience knows that Brutus will be successful in his "enterprise", but that it is not the business in which Portia thinks her husband is involved.