어디야? - where are you?
and 어딘데? - where are you? where is it?
1) 어딘데 is a Kyungsang-do dialect. It means 'where are you?'
2) 어딘데 is short for ''어디인데?'' (If a person who speaks stardard Korean says this)
it might sound '어딘데?'
Situation 1. (Where are you?)
A and B are supposed to meet at 1 pm
A: I will be late about 30 minutes.
B: WHAT? 어디인데? The meeting is very important and about to start in 5 minutes.
A : Sorry. I just passed the xx department store.
* Please focus on the nuance and tone.
Situation 2 (Where is it?)
A : I found a nice Korean restaurant.
B : 어디인데?
A : The opposite of the xxx station.