Bonjour Sukanya ! Actually, to say "What are you talking about?" in French, you need to remember that we use "parler DE [quelque chose]", therefore the question would be: "De quoi est-ce que tu parles ?" However, you can also use the verb "dire" to express "What are you saying?": "Qu'est-ce que tu dis ?" I hope that's helpful! À bientôt !