About what are you talking?

To put this thing simple… is that kind of sentence GRAMMATICALLY correct? I know that nobody’d say anything like that but as far as grammar and only grammar is concerned… is it correct?

Just an excerpt from the chapter on Wh-questions (Who,What,Which,Why,…):“Begin with the Wh-question word or phrase, then use the interrogative pattern: operator + subject + rest of the VP (verb phrase). Questions on the pattern Who did you give it to? are very frequently heard. All the commonly used prepositions could fit into that pattern, except ‘since’ and ‘during’, which are placed before the Wh-question word, (…) The pattern To whom did you give it? can be used with all prepositions though it is typical of formal style.”
That is, more colloquial would be:" What are you … about?"

As far as grammar is concerned, the sentence is correct because it doesn’t break any known grammar rule.
But on the flipside, not everything that is grammatical reads well. And your sentence doesn’t read well, as you must realise.