it represents jem's childhood
When Calpurnia says Jem has the "look arounds," she means he's behaving suspiciously or behaving in a way that suggests he's up to something. It implies that Jem is acting in a sneaky or curious manner.
yes jem is courageous
Jem's response "In a pig's ear you did" is slang that means disbelief or skepticism, similar to saying "I don't believe you" in a playful or sarcastic way. Jem doesn't think that Dill actually helped engineer the train; he is expressing doubt about Dill's claim.
When Miss Maudie says that Jem gets more like Jack Finch every day, she is implying that Jem is becoming more mature, responsible, and thoughtful - traits that are characteristic of his Uncle Jack. It suggests that Jem is growing into a respectful and wise young man, similar to his uncle.
Boo Radley saves Jem and Scout in Chapter 29 of "To Kill a Mockingbird" when he emerges from his house to defend the children from Bob Ewell's attack. Boo intervenes and ultimately saves Jem and Scout from harm.
he attacks Jem which breaks Jem's arm, then is stabbed, presumably by Jem or Boo Radley, who brings Jem back home
Dill and Jem see the shadow of Atticus Finch when Jem is on the porch of the house.
When Jem says "it ain't right," he is expressing his belief that something is unjust, unfair, or morally wrong. This shows his sense of empathy, moral compass, and desire for justice.
a camellia flower, like the ones of hers that Jem destroyed earlier. She did that to show Jem that she wasn't as awful of a person as Jem (and Scout) believed she was.
Jem from Jem and the Holograms is a fictional character. Her real name is Jerrica Benton, who leads a double life as a music superstar.
Atticus meant that Jem had almost made a false statement damaging someone's reputation, which is a serious offense. He was cautioning Jem to be more careful with his words so as not to harm others unjustly.