One of the most fundamental sentence from the English “phrasebook” that almost every beginner will learn is this sentence, using which one can ask another one’s nationality or country/region of origin. However, this sentence has always troubled me.
The word where is an adverb in this context, and it functions as an adverbial; from is a preposition, and it functions as part of the subjective complement in this sentence. Id est, when responding to this clause, people may say, for example, “I am from Milan.” Now, in that response, I is a pronoun functioning as the subject, and the rest of the sentence, am from Milan, is the predicate, which is comprised of the copula, or the linking verb, am, and the subjective complement, from Milan, which is a spatial adverbial.
What I have learned about English grammar prescribes that an interrogative/relative adverb, such as where or when, cannot follow a preposition, because an adverb alone functions as an adverbial, and the structure “preposition + noun/pronoun” ought to correspond to an adverb. Id est, the phrase from Milan (preposition + noun) can and should correspond to that adverb where, and structures such as from where are illegitimate.
I think it is fairly common that adverbs do not follow prepositions. People always say clauses such as where are you at is grammatically incorrect, because at is a preposition and where is an adverb, so it should simply be where are you. Therefore, what troubles me is that why the phrase where are you at is incorrect and criticized, while I have not seen people avoiding where are you from.
In my humble opinion, the canonical form of this clause should be from which country/region are you, or at least which country/region are you from, but it seems awfully pedantic and there is a highly probable chance that the utterer will get thrashed…