How did Jean get the nickname of "Scout"?
Harper Lee does not directly comment on the origins of Scout's nickname throughout the novel, but one can surmise that Atticus gave Scout her nickname because of her vibrant, curious personality. Jean Louise is referred to as Scout because she is an inquisitive, brave girl, who is continually observing and inquiring about the world around her.
Throughout the novel, Scout asks various adults, most notably Atticus, to explain and elaborate on certain topics that she does not fully understand. For example, Scout inquires about Boo's background in chapter 5 and asks Atticus and Calpurnia to define several explicit terms.
Aside from her curious nature, Scout is also a brave girl, unafraid of physical confrontations and readily engaging in fights towards the beginning of the novel. She also endures criticism from her fellow community members regarding her father's defense of Tom Robinson. She courageously sneaks into the Radley's backyard at night and unknowingly enters a dangerous situation because of her curiosity in chapter 15.
Scout is also a very observant young girl. Following the Tom Robinson trial, Scout notices the overt prejudice and hypocrisy throughout her community. Scout begins to question the character of certain racist community members and develops perspective on the world around her. Overall, Jean Louise's curious, courageous, and observant personality earns her the nickname "Scout" throughout the novel.
While not directly stated in the novel, Scout's nickname comes from her innate curiosity and willingness to question why things are the way they are. She teaches herself to read, an indication of her intelligence, and is constantly trying to understand the world around her. She does not hesitate to question others in her search for meaning and information. This is a characteristic encouraged by her father, Atticus, who answers Scout honestly, even when she asks difficult questions, and allows her to be exposed to situations which many other children would be sheltered from. For example, she asks him what "rape" is, & he replies with a definition that does not condescend or mock her.
Scout also likes to explore sides of life that she would traditionally be taught to avoid. She hates wearing dresses, and could definitely be considered a "tomboy". She is eager to accompany Atticus to Helen's house, & to accompany Calpurnia to church. She is blazing a trail for moral justice in her life, making her nickname well-earned.