How long have you been living in oxford is correct sentence?

The sentence "How long have you been living in Oxford?" is grammatically correct.

However, it's important to consider the context.

* If you are asking someone about their residency in Oxford, the sentence is perfect.

* If you are asking about the history of the city of Oxford itself, the sentence wouldn't be correct. You'd need to say something like, "How long has Oxford been a city?"

Always remember to think about the meaning you're trying to convey.