The English should be "What is your nationality." "Citizenship" may be correct strictly speaking, but English speakers don't use the word the way Duo uses it in this lesson. Too bad nobody at Duo seems to be paying any attention to the Vietnamese module these days. Nothing is likely to get fixed.
While I completely agree with the preceding comments, it's erroneous thinking on our part: most of the world doesn't have birthright citezenship, and thus your nationality might be different than your citizenship. Also, many people have dual citizenship...
As an American, it sounds funny to my ears, but if a Vietnamese person asked me this, this would be what they were actually asking... I think.