Ответ:
1. Who will take part in a music contest? Where our singer will take part?
2. What I had just finished? When I had finished my work?
3. Who have never faced such a problem? Did we faced such a problem?
4. When she performed a brilliant show? What did she perform yesterday?
5. What does Khadija like? What does she have to do with music?
6. Whose play they had recently performed? How often they had performed William Shakespeare's play?