When does Jem apply one of Atticus's lessons in To Kill a Mockingbird?

Jem applies one of his father's lessons from Chapter 3 when he learns of Dill's having run away from home and he alerts his father that Dill is in Scout's bedroom.

Earlier in the narrative, Atticus advises Scout,

"You never really understand a person until you consider things from his point of view....until you climb into his skin and walk around in it." (Ch.3)

In Chapter 14, Dill Harris runs away from home in Meridian, Mississippi, and hides in the Finch house in Scout's bedroom. When she and Jem are made to retire early for the night, Scout steps on something by her bed that is "warm, resilient, and rather smooth." So, in fear she goes to Jem's room, saying she thinks there is a snake under her bed. Jem rises and gets a broom from the kitchen so he can sweep under Scout's bed. He makes a couple sweeps under the bed, and hears a grunt. It is no snake; it is Dill, all brown with dirt and caked mud.

After requesting food, Dill concocts a tall tale about having been chained to the basement wall by his step-father who wants him to die. "How'd you get here?" Jem asks, interrupting Dill's tale. In truth, he has taken the train and ridden on the back of a cotton wagon to Maycomb's outskirts; then walked the rest of the way. Once at the Finches' house, Dill entered and hid under Scout's bed.

"They must not know you're here," said Jem. "We'd know if they were lookin' for you..."
"Think they're still searchin' all the picture shows in Meridian," Dill grinned.
"You oughta let your mother know where you are," said Jem. "You oughta let her know you're here..."

Scout is appalled when Jem "broke the remaining code of our childhood" by walking down the hallway and calling to his father. For, Jem is mature enough to realize that Dill's mother must be very worried about his whereabouts. Now, he has followed his father's advice of considering things from another person's point of view and "walking in [her] shoes." Certainly, Jem has "climbed into the skin" of Dill's mother and understands the worry and concern she must have for Dill's safety, so he alerts Atticus, who can get in touch with her. Indeed, he has applied one of Atticus's valuable lessons.