From your reading of the play, what have you learned about ambition?
I can't really tell you what you learned about ambition from reading Shakespeare's Julius Caesar. I can only tell you what the play reveals about ambition.
First, Caesar is assassinated, in part, because others (at least Brutus) think he's ambitious. Caesar was wealthy, successful, and well-liked, and wielded a great deal of power in ancient Rome. Yet, some thought he wanted more.
Though Caesar was possibly ambitious and may have eventually accepted the crown that would make him emperor, some of those who killed him were certainly ambitious. Cassius, in particular, accepts bribes, as Brutus calls them, increasing his own wealth due to his new position of authority.
In short, then, ambition leads to assassination and taking bribes in the play. It seems that many of the conspirators killed Caesar not because of his ambition, but because of their own ambition.