In To Kill a Mockingbird, what other character would be the best choice to give Jem advice apart from Calpurnia, Atticus, and Miss Maudie?
Jem didn't get to meet Dolphus Raymond along with Dill and Scout on the day of the trial, but I'm sure the children never forgot their visit with the evil but fascinating man. It was clear that Dolphus had great respect for Atticus, telling Scout that
"... you don't know your pa's not a run-of-the-mill man, it'll take a few years for that to sink in--you haven't seen enough of the world yet."
But Jem was a bit older, and he may have benefited from a long conversation with Dolphus--and a sip of Coca-Cola from the sack. Like Atticus, Dolphus knew beforehand what kind of verdict would be rendered, and Jem and Mr. Raymond could have shared their views on the jury--and Jem may have learned a few more secrets about his father from the eccentric man from one of Maycomb's oldest families.
Jem is conflicted in the the later chapters of To Kill a Mockingbird. He is angry and confused due to the racial segregation that is prevalent in the setting of To Kill a Mockingbird which takes place in rural Alabama during the Great Depression. Amidst this backdrop Jem's father Atticus decides to defend an innocent black man who is accused of raping a white woman. The rest of the town automatically assumes the guilt of the black man, and Atticus is labeled a nigger lover. Jem is angry and confused because of this. The best advice for Jem would be to listen to his heart and to trust his father.