In To Kill a Mockingbird, I've only found two examples when the idea "You never really know someone until you walk in their shoes" is referred to....

There is a second time when Atticus refers to his famous quote about walking in another person's shoes.  Bob Ewell threatens Atticus after the trial.  This concerns Jem.  He is worried that Mr. Ewell will do something to harm his father.  He wants his father to do something about it as a precaution.  Atticus reasons with his son:

"Jem, see if you can stand in Bob Ewell's shoes a minute.  I destroyed his last shred of credibility at that trial, if he had any to begin with. The man had to have some kind of comeback, his kind always does."

Atticus then goes on to say that he is willing to listen to Mr. Ewell's threats if it will save his daughter from being beaten.  Atticus says that Mr. Ewell is going to take his anger out on someone, so he would much rather it be on him then on the man's children.  After his father explains the situation in this way, Jem finally understands.  

Even though Mr. Ewell threatens Atticus, he seeks to understand the man.  He wants his son to consider that Mr. Ewell was probably ashamed at the trial.  This is because Atticus discredited Mr. Ewell's arguments during the trial.