Where in Harper Lee's To Kill a Mockingbird can the following passage be found: Atticus says you can choose your friends but you sho' can't...

In Harper Lee's To Kill a Mockingbird, Jem speaks the lines in question close towards the end of Chapter 23, approximately 4 pages from the end of the chapter.

Chapter 23 opens with Atticus having just been spat in the face and threatened by Bob Ewell near the post office. The incident leads Jem and Scout to discuss with Atticus their fears of Ewell. After Atticus asserts they have nothing to fear, the conversation turns to Tom Robinson's case and his prospects of being acquitted by the higher courts upon appeal. Jem and Atticus also have a heated discussion about the unfairness of the jury system, especially the fact that the jury decides the penalty in capital cases, not the judge. The conversation then turns to the fact that Atticus intentionally let a kinsman of the Cunninghams remain on the jury, a Cunningham who nearly acquitted Robinson. The revelation concerning the Cunningham jury member leaves Scout feeling a slight sense of admiration for the Cunninghams. It's at this moment that Scout announces she is going to invite Walter home for lunch once school starts, prompting her Aunt Alexandra to refuse permission. In explanation, Aunt Alexandra states, "Jean Louise, there is no doubt in my mind that they're good folks. But they're not our kind of folks," meaning that they are from a lower class in society than the Finches.

Scout feels extremely offended by her aunt's notion that the Cunninghams should be shunned. As a retort, Scout asks if she could invite Walter home "if he was kin to us" to which her aunt replies that he still could not be invited into the Finch home even if he was a kinsman. Equally feeling offended by their aunt's prejudiced judgements and shallowness, Jem replies with the passage in question:

Aunty, ... Atticus says you can choose your friends but you sho' can't choose your family, an' they're still kin to you no matter whether you acknowledge 'em or not, and it makes you look right silly when you don't. (Ch. 23)

Though Jem's response does nothing to change their aunt's mind, it certainly shows how ridiculous Aunt Alexandra's prejudiced views are and the views of people like her. Hence, all in all, the passage in question serves to develop Harper Lee's themes concerning prejudices and family.