I am asking my friend on mobile.
Where are you now? or, Can I ask him,
Where are you at now? Which one is more correct?
Thank you.
I agree with Mr_Ben, "Where are you at?" is completely foreign to me.
Among young people it certainly is. "Where are you" sounds incomplete to me, but I realize it's preferred in formal English.
For arguments for and against "Where are you at," see Where are you (at)? « Motivated Grammar.