To kill a mockingbird: who is sure during the whole trial that atticus and tom will win the case?

Jem Finch.

Explanation:

"To Kill A Mockingbird" by Harper Lee is about the story of the residents of Maycomb and the various issues prevalent during that time in the southern part of America. Atticus Finch and his children Jem and Scout are the primary characters, along with other major characters and minor characters.

One of the characters, Tom Robinson has been accused of sexually assaulting a white girl, Mayella Ewell. This was a serious case for Tom was black and the issue of racism is still common in America. Atticus, as a lawyer, represents the accused. Jem is so sure his father and Tom will win the case for he knows what a good man his father is. Also, he and his sister had always thought that everyone in their town are good people, representing only goodness in them like their father is. They haven't really experienced any case of bad behavior or bad characterization in anyone. Jem may have also known a bit about the truth of the case as his father is the lawyer of the accused. But overall, his assurance of the victory of Atticus and Tom most probably stems from his strong belief in the overall goodness of people.