Translation:Where are you?
From my experience, Northern Chinese use 哪兒 nǎ'er more often. Southern Chinese use 那裡 nàlǐ more often.
Yes I was wondering the same thing. 哪儿 or 哪里. What is the difference?
Taiwanese and probably a lot of southern Mainland Chinese tend to say 哪里, while northerners typically say 哪儿。那里 and 那儿，这里 and 这儿 are the same difference.
My roommate at CET in Beijing in the summer of 1992 told me I said this in my sleep once.
From a spoken phrase, how do you differentiate between 你在哪里 (Where are you?) and 你在那里 (you are there)
I think it would be 你在那里吗 (or 你在那儿吗) . I believe the 那 ('there') is fourth tone; 哪 ('where') is third.