The proper phrasing to ask the question “where you are” in archaic English is “where art thou?” This is specifically for if you are asking a question. If you state where someone is, you can use “where thou art.”
Where Art Thou vs Where Thou Art
“Where art thou” implies a question, whereas “where thou art” represents a statement. While we no longer use “thou” in common English, we still differentiate similarly. This is because the grammatical structures we use today are similar in verb placement to the more archaic English used in these phrases.
In contemporary English, we would ask someone, “where are you?” In this case, you replace the verb “art” with “are” and “thou” with “you.” If I wanted to say where someone is, I could say, “Where you are…”
Similarly, in a description of a place with older English, one could say, “Where thou art…” This phrasing is less standard but is still functional. It is just used in different cases than “where art thou”
In “where art thou?” the verb of the sentence is art. The subject of the sentence is “thou” meaning “you.” In that phrase, the subject is after the verb. Usually, the subject is before the verb in a sentence. However, to emphasize that a sentence is a question, writers and speakers can switch the two. This is called inversion and it is common in many languages, including English.
Examples
The following examples can clarify the common usage of the phrases “where art thou?” and “where thou art.”
O Brother, Where Art Thou?
O Brother, Where Art Thou? Is a crime comedy film made in 2000. The title helped popularize the phrase “where art thou?” You can see from the title of this film that it is a question. The speaker is asking the “brother” where they are. The question is a direct translation of “where are you?” simply using a term for “you” that is no longer in the common vernacular.
Where Thou art—that—is Home
Where Thou art—that—is Home is a poem by Emily Dickinson from around 1863. In the title and first line of this poem, Dickinson writes a phrase that essentially means “wherever you are is my home.” The sentiment is familiar to all audiences. In this phrase, the subject, “thou,” is directly after “where.” This placement makes it a statement rather than a question.