Learn Spanish (Latin America): Los espectadores no saben de qué se trata la exposición abstracta. - The viewers do not know what the abstract exhibition is about.

The current lesson contrasts the personal tratar de (to deal with) and the impersonal tratarse de (to be about). According to strict traditional grammar, if a sentence has a specific subject like la exposición abstracta, you should use the personal form without the pronoun: de qué trata la exposición. However, in conversational Latin American Spanish, it is incredibly common to use the pronominal form tratarse de even when there is a subject, meaning "to be about" (e.g., la exposición se trata de...). This sentence perfectly captures that natural, everyday Latin American usage!

Why does the sentence say de qué instead of putting the de at the end like the English translation "what ... is about"?

In Spanish, a clause or sentence can never end with a preposition. Since the verbal phrase is tratarse de (to be about), the preposition de must stay glued to the front of the question word qué. Therefore, the English structure "what it is about" must be rearranged in Spanish to "about what it is about," resulting in de qué se trata.

We have no saben, which expresses a lack of knowledge. Why is se trata in the indicative mood rather than the subjunctive?

Although negative statements with verbs of knowing or believing (like no creer or no pensar) often trigger the subjunctive, this sentence contains an indirect question. You can spot this because of the question word qué. Indirect questions in Spanish almost always take the indicative mood because they are simply reporting what the question itself is, rather than expressing subjective doubt about a specific action taking place.