What are you talking
I saw when “talk” used as transitive verb ，it has the same meaning as “talk about” 。
For example：to discuss or chat about (a topic): [~ + about + object]
We talked about the movies . [~ + object] to talk politics.

So I want to know whether “what are you talking” is correct

Question

What are you talking
I saw when “talk” used as transitive verb ，it has the same meaning as “talk about” 。
For example：to discuss or chat about (a topic): [~ + about + object] 
We talked about the movies . [~ + object] to talk politics.

So I want to know whether “what are you talking” is correct

Answer

You would say: What are you saying?
OR: What are you talking about?

Answer

Hi Cis:

Another way to express this idea is this:  "What are you discussing?"

Answer

No- you would always say "what are you talking about".

And while "to talk politics" is correct, usually people say "to talk about politics". The transitive form you mention is somewhat uncommon.(though still used occasionally)

Answer

It should be "What are you talking about?". 
We use talk+to sb
talk+about sth or sb
We use talk in conversational exchanges & while communicating informally.