Yes/ No questions:

S + asked + O + if/ whether + S + verb (lùi thì)

Wh-questions:

S + asked + O / wondered / wanted to know + Wh-questions + S + verb (lùi thì)

10. Lan said to me : “Did your father work for a foreign company 3 years ago?”

--> Lan asked me if my father had worked for a foreign company 3 years then.

11. “Can people wear the Queen’s and King’s clothes for a while?”, she said to me.

--> She asked me if people could wear the Queen’s and King’s clothes for a while.

12. She said : “Can you speak Spanish, Minh?

--> She asked Minh if he could speak Spanish.

13. Thanh said to her teacher : “Will I finish my exercise at home?’

--> Thanh asked her teacher if she would finish her exercise at home.

14. They said to us : “Must you go now?”

--> They asked us if we had to go then.

15. I said to Mr. and Mrs. Thanh : “Will you go to Nha Trang on your holiday next month?’

--> I asked Mr. and Mrs. Thanh if he and she would go to Nha Trang on his and her holiday the following month.

16. She asked me : “Have you done your homework yet?”

--> She asked me if I had done my homework yet.

17. Nien asked Hoa: “Have you done your homework yet?”

--> Nien asked Hoa if she had done her homework yet.

18. “Have you read this information yet, Hoa?” Lan asked.

--> Lan asked Hoa if she had read that information yet.

19. “Have you had enough for lunch?” the landlady asked us.

--> The landlady asked us if we had had enough for lunch.

Mình hơi rối ở câu 15 nên mình sai thì bạn sửa dùm. Thanks!