What quotes from Harper Lee's To Kill a Mockingbird show that Scout is a tomboy?

“I should think so. She eats all the leftover fingers and ears from the hospital.”

“Aw, that’s a damn story,” I said.

“I beg your pardon?”

But at supper that evening when I asked him to pass the damn ham, please, Uncle Jack pointed at me. “See me afterwards, young lady,” he said.

In the above quotes, Scout and Uncle Jack are discussing the latter's cat, Rose Aylmer. During the conversation, Scout uses the words "damn" twice, and this upsets Uncle Jack. After dinner, Uncle Jack tells Scout that she's more like Atticus than like her mother. He advises her to be vigilant about the language she uses so that she can grow up to be a lady.

In this exchange, Uncle Jack implies that girls who want to grow up to be ladies should not curse. Scout, however, does not particularly want to grow up to be one. According to the conventions of her time, Scout would be considered a tomboy.

But I was more at home in my father’s world. People like Mr. Heck Tate did not trap you with innocent questions to make fun of you; even Jem was not highly critical unless you said something stupid.

In this quote, Scout admits that she feels more comfortable in the world of men. Although she knows that she is expected to relish her initiation into feminine society, Scout confesses that "ladies in bunches" always fill her with "vague apprehension and a firm desire to be elsewhere." Because of her decided preference for her father's world, Aunt Alexandra characterizes Scout as a "spoiled" little girl. 

Aunt Alexandra's perspective is indicative of the attitudes of her time. Again, according to convention, Scout would be considered a tomboy. 

“Reckon you’re at the stage now where you don’t kill flies and mosquitoes now, I reckon,” I said.

“Lemme know when you change your mind. Tell you one thing, though, I ain’t gonna sit around and not scratch a redbug.”

“Aw dry up,” he answered drowsily. Jem was the one who was getting more like a girl every day, not I.

In this humorous exchange, Scout is irritated with what she believes is Jem's increasingly baffling and volatile behavior. When she tries to kill a bug, Jem lectures her against doing so. Jem's high-handed attitude annoys Scout, and she declares that Jem is "getting more like a girl every day."

Here, Scout implies that Jem is getting "soft" or becoming more effeminate; after all, it is not customary for boys to concern themselves with the ethical implications of killing a bug. Scout's words demonstrate that she identifies with the male perspective more often than she does the female one. Again, according to the conventions of her time, Scout would be considered a tomboy.