The passages that you are looking for can be found in chapter 12, where Calpurnia takes Jem and Scout to her church, because Atticus is out of town. During their visit to Cal's church, Scout is startled and intrigued by many new facts that arise. She finds out, first of all, that Calpurnia changes her dialect whenever she is around her black friends. When she is at Scout's house, she talks like Scout and Jem talk, but when they arrive at the church, Cal changes her speech. When she questions Cal about this, Cal states,
"if I talked white-folks' talk at church,...they'd think I was puttin' on airs to beat Moses."
The next thing that Scout learns is that most of the black people attending the church cannot read or write. She wonders about this as they are about to sing a hymn, and can't find a hymnal; she asks, "How're we gonna sing it if there ain't any hymn books?" She soon learns that Zeebo-who can read-sings out one line that everyone else then echoes. A couple other startling facts: Scout realizes that Tom Robinson's wife is having a rough time since Tom is in jail, and that the people of her church are helping her out through monetary donations. She also learns that Cal doesn't know how old she is, because of black people being illiterate and not taking much stock in a calendar. She also learns, through the impertinent comments of Lula, that some black people don't really welcome white people in their neighborhoods. So, Scout learns an awful lot in the couple of hours that she is at Calpurnia's church, and takes it all in with her usual curious questions.