The kwiz question is: Cristina no sabe todavía ________ va a celebrar su cumpleaños.
The most import possibilities are dónde and donde.
If i look in the lesson: Difference between dónde and donde (with and without a written accent)
i see: if you can substitute it for "in what location", you can use dónde.
This answer was wrong, it should be donde. I don-t understand that, it seems to contradict the lesson.