Should I say "Where are you at now?" or "Where are you now at?"
Which is grammatically correct? And is there any difference in meaning between the two?
Both are possible in speech, although the first is probably more likely. They can be:
a) an inquiry about someone's location;
b) an inquiry about someone's mental, spiritual or emotional state; or
c) an inquiry about which page someone has reached in a book.
Neither example feels very comfortable grammatically although I feel this is perhaps a BE view. We used to say 'a preposition should never be used to end a sentence with.' In fact, the use of at in either case seems redundant since both examples make sense without it.
Neither is correct. Never end a sentence with the word "at". "Where are you now?" Or "Where are you?" There is no reason to add "at" to this sentence.