"Do you want?"
Officially it's the rotated or turned comma. I think U+02BB is the correct one. If you're on PC you can use the Character Map or shrink your screen (the extra marks and letters should be at the bottom, but may be pushed under the bottom edge). If you are on a mobile device, you'll have to find out how it works for your device in general (not just duolingo). On my phone I can just hold on a letter (in this case the apostrophe) to be offered variations. Some phones require you to switch to a Hawaiian keyboard or things like that.
Mahalo - I have tried this app on my iPhone and used every conceivable quote-looking character that I could find on one level. It was frustrating since there was no way I could advance beyond that particular level. Gave up and returned to using the website where I could proceed with just a warning.
I think I have also used the apostrophe (non-shifted double quote key next to "return" on most keyboards) on some answers and it didn't complain. (e.g. "Kai'ulani")
Chalking it up to version being an early version of this language...