Translation:Where is my passport?
'我的護照在那兒？' should be 'Is my passport there?' since 那兒 = there. However, their correct sentence is 'Where is my passport' which should be '我的護照在哪兒？' instead.
This is in fact traditional Chinese other than simplified Chinese. This course emphasizes simplified version more than traditional.
Yes. Sorry for that since my keyboard can only type traditional Chinese. Anyway, it still doesn't change the fact that 那 = there and 哪 ＝ where.
According to Wiktionary at https://en.wiktionary.org/wiki/%E5%93%AA#Chinese, "哪" is both the simplified and traditional form for "where".
Wiktionary also lists "那" as an alternate form of "哪" at https://en.wiktionary.org/wiki/%E9%82%A3#Etymology_2 though, which I wasn't aware of, so I guess this is good practice.
Edit: I somehow missed that the "那" entry has a "(dated)" annotation.
Many mistakes on Duolingo Chinese...
那儿 there / 哪儿 where
我的护照在哪儿？ Where is my passport?
我的护照在那儿！ My passport is there!
我的护照在那儿吗？Is my passport there?
Five months and no one has fixed most basic mistake? Clearly no one has looked at the reports on this for five months.
Once you realise that your proficiency in the foreign language you seek to learn is greater than that of those who put together the duolingo exercises, it's time to look for somewhere else to learn.