It is grammatically correct to say: There is nothing wrong with this machine. It is not grammatically correct to say: Will it is be grammatically correct to say .... The correct way to write that or say that would be: Would it be grammatically correct to say....
It is not, but it is widely used because it conveys the general idea of the question as well as its grammatically correct version. No you should say "Where are you" the at at the end is not needed.
'Were you' is grammatically correct, as it gives us a subject (you), and a time (past), although it is not a full sentence, which requires a location. So you could say 'Were you upstairs?' and it be a 100% grammatically correct English sentence.