There are many instances of discrimination--both racial and social--in To Kill a Mockingbird, and I would consider any use of the "N" word to show it.
MISS GATES. (Scout recalls a conversation she overheard by her teacher, Miss Gates). "... they were gettin' way above themselves, an' the next thing they think they can do is marry us."
BOB EWELL. (to Atticus) "To proud to fight, you nigger-lovin- bastard?"
AUNT ALEXANDRA. (to Scout, concerning Walter Cunningham Jr.) "Because--he--is--trash, that's why you can't play with him."
MAYELLA EWELL. "That nigger yonder took advantage of me..."
LULA. (to Calpurnia at church) "You ain't got no business bringin' white chillun here--they got their church, we got our'n."
MRS. DUBOSE. (about Atticus) "Not only a Finch waiting on tables but one in the courthouse lawing for niggers!"
COUSIN FRANCIS. (about Atticus) "I guess it ain't your fault if Uncle Atticus is a nigger-lover..."
Jem: "Why dont you get a coloured man?"
Cecil Jacob : "Scout Finch's daddy defended niggers."
Atticus : "there's been some high talk around town to the effect that I shouldn't do so much about defending this man"
Atticus : "The jury couldnt possibly be expected to take Tom Robinson's word against the Ewells"