Not at the end of a sentence that starts with Where, I hope!
Where are you at? is redundant. Both where and at ask the same location information, so the question should just be Where are you?
I know this usage is ubiquitous, among all ages and any other group distinctions you care to make. That doesn’t make it grammatical. I’m also aware that it has a long history. That still doesn’t make it grammatical.
Yes, we use informal grammar all the time (I won’t criticize your ain’t), but if you’re going to use wrong constructions, do so intentionally, not accidentally.
Of course, my criticism of at ending a sentence that begins with Where does not apply to one that begins with What.
What are you looking at? is just fine and should not be awkwardly manipulated to read At what are you looking? just to satisfy some pedant’s misinformed “rule” about not ending a sentence with a preposition. (See my Tip on that eventually.)
The next time you’re tempted to ask Where are you at?—please don’t! Just ask Where are you? instead.
If I’ve managed to stop just one usage, I’ll consider this a successful post. Maybe it will catch on.