I think that, overall, we see that Curley thinks that his wife is his property because of how he is always running around looking for her. He seems to expect that he has the right to know where she is at every moment. He seems to think that he owns her and that she should not go places without letting him know. You should also note that she doesn't even get her own name -- that implies she's nothing but his.
As for a specific quote, I would use one that is on page 62 in my book. This is where Curley and Slim are arguing. Slim is telling Curley that he should tell her to stay where she belongs. He is saying that Curley should control her better. That sounds more like someone talking about a dog than about a person.
In Steinbeck's Of Mice and Men, on page 94 of my copy of the book, Curley's wife tells Lennie why George says Lennie shouldn't talk to her:
She said quietly, "He's scared Curley'll get mad. Well, Curley got his arm in a sling--an' if Curley gets tough, you can break his other han'. You didn't put nothing over on me about gettin' it caught in no machine."
She adds a minute or so later:
"I get lonely," she said. "You can talk to people, but I can't talk to nobody but Curley. Else he gets mad. How'd you like not to talk to anybody?"
Curely treats his wife like she is a piece of property, like he owns her. He limits what she can do and who she can talk to--or at least he tries. She is kept on the property and told what to do.
Actually, however, the most important quote and detail that shows Curley's wife is treated with disrespect is the fact that readers have to refer to her as "Curley's wife," since she isn't even named in the novel.