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 !