I saw this sentence when I was watching a TV play. I don't understand what it means. The heroine said this to the hero. My brother thinks this sentence means "you don't understand". However, I think this sentence means "you know". So we quarreled. I need you to help me understand what this sentence means.
I asked my friend. He told me that this is a Chinese rhetorical device called "double negation means affirmation". I don't understand this rhetorical device. I hope you can provide more such sentences.