In "To Kill A Mockingbird," who uses the 'N' word ?

Just about everyone in the book uses the 'N' word at one time or another. Miss Maudie doesn't at any point, and neither does Aunt Alexandra, Calpurnia, Boo, or Mr. Dolphus Raymond. Most of the black people don't use it, either, with the exception of Tom Robinson himself when he says in the trial to Mr. Gilmer, "It weren't safe for a nigger like me to be in a--fix like that," and Lula, when Calpurnia takes Jem and Scout to church with her one Sunday, who says, "I wants to know why you bringin' white chillun to nigger church." 

Even Atticus uses it a couple of times, but each time he points out, overtly or subtly, that it's a word they don't use. When Scout asks him, "Do you defend niggers, Atticus?" He responds, "Of course I do. Don't say nigger, Scout. It's common." 

Mr. Gilmer doesn't actually say it, either, but he uses all the language cues that suggest he would in other circumstances (outside of a trial), calling Tom Robinson "boy," for example. 

The men from Old Sarum who surround the jailhouse the night Atticus is sitting watch to hopefully prevent a lynching don't actually use the word, but they clearly use it in normal circumstances--since they're clearly there to lynch Tom. 

Mrs. Dubose accuses Atticus of "lawing for niggers," and Bob Ewell accuses Atticus of being "nigger-lovin' trash," and Mayella uses the word when she says that "that nigger took advantage of me." 

Just because a person doesn't use the word in the novel doesn't make them non-racist, though.