How is Jem similar to Atticus in To Kill a Mockingbird?

In one specific episode in Chapter 10, Jem declares that his father is just like him: he is a gentleman who does not take advantage of others.

When the children are given air-rifles for Christmas, Atticus will not teach them to shoot, so Uncle Jack instructs them in the basic operation of their guns. He tells them that their father does not like guns. Later on, they learn why. 

One Saturday Jem and Scout decide...

In one specific episode in Chapter 10, Jem declares that his father is just like him: he is a gentleman who does not take advantage of others.

When the children are given air-rifles for Christmas, Atticus will not teach them to shoot, so Uncle Jack instructs them in the basic operation of their guns. He tells them that their father does not like guns. Later on, they learn why. 

One Saturday Jem and Scout decide to explore the area with their air-rifles to see if they can find a squirrel or rabbit. Instead, Jem spots a dog staggering down the street. Scout recognizes it as Tim Johnson, the liver-colored dog of Mr. Harry Johnson, the driver of the Mobile bus. Because the dog is staggering, Jem decides to alert Calpurnia. When the maid sees this dog, she hurries the children home and immediately phones Atticus who soon arrives with Sheriff Tate. After the men see the dog, they realize that he is rabid and must be shot.

"Take him, Mr. Finch." Mr. Tate handed the rifle to Atticus; Jem and I nearly fainted. 
"Don't waste time, Heck," said Atticus. "Go on."
"Mr. Finch, this is a one-shot job."

Sheriff Tate implies that he is not as accurate a shot as is Atticus. Then, he tosses the rifle at Atticus, who complains that he has not fired a gun in thirty years. Nevertheless, he pushes his glasses up to his forehead, takes aim, and fires a shot; this shot is a direct hit, and the poor dog crumples onto the sidewalk. Jem is amazed.

"I saw that, One-Shot Finch!" calls Miss Maudie. Jem remains in "numb confusion" for a few moments, then he recounts aloud what has just happened. In response to his amazement, Miss Maudie explains to Jem why she has referred to Atticus as "One-Shot," adding that Atticus began to think that God had given him an unfair advantage over most living creatures. Therefore, he decided not to shoot anything unless he had to do so.

"Looks like he'd be proud of it," Scout says. But, Miss Maudie disagrees: "People in their right minds never take pride in their talents." When she says this, Jem realizes something important about his father. With great admiration, he exclaims, "Atticus is a gentleman, just like me!"