It means like a swift come back, say in the instance if someone is rude to you around your friends and your friends tell you "yo clap back!" You have to respond with a better come back. Also if you are interested in any slang words or phrases there's a website called urban dictionary it helps with those a lot.

Sorry it's a typo. Yahoo news used such word frequently like "clapback at one's opponents/enemy"

does, not dose. If you want to sound more natural, don't drop your pronouns like you do in Chinese!

No idea. Native speaker forums? Can you give a reference?