What does Tom Sawyer tell Becky he wants to do when he grows up?

When he testifies against Injun Joe to clear Muff Potter's name, the way he stood up for becky and told the teacher that he was the one who ripped the book, letting aunt polly know that he is save on the island, having kindness towards injun Joe when they find him dead in the cave, because he knows how much he suffered in there.

Also when he sees hi aunt cry in the funeral, he get sad, and when he has the nightmare for Becky: he dreams Injuin Joe killing her.