Dill is a child with a tender heart. The reader first sees evidence of this early in the novel when Jem compares the task of getting Boo Radley outside to making a turtle come out of its shell. He says a turtle will come out if a match is struck underneath it. Dill says that this act would be "hateful." Later, during Tom Robinson's trial, Dill has to leave the courtroom because he starts crying. He becomes upset with how the prosecuting attorney speaks to Tom in a demeaning and disrespectful way. After the trial, Dill states that he would like to be a clown when he grows up. He is disappointed in Tom's guilty verdict and says that, "There ain’t one thing in this world I can do about folks except laugh." His plan is to join a circus and laugh at people although Jem attempts to explain to Dill that he has it "backwards." Jem says people laugh at clowns. It matters little to Dill. He simply replies that he will be a "new type of clown."

I think you are asking what Dill wants to be when he grows up. At one point he asserts that he would like to be a clown.

This matches his character for 2 reasons. On the one hand, he enjoys being an entertainer. The kids call him a pocket-merlin because he magically plays roles very quickly. On the other hand, he is a gifted and talented liar. He tells stretchers, big ones (according to Scout). And he wants to make people laugh.

Later in the story, he reports working on the railroad as an engineer with his dad (who we don't believe that he really has).