Kindly, consider the following two sentences:
1) In a situation that a manager is telling a person who is applying for the job: "You have to prove that you are the right person for the job." What is the correct question tag for this statement, is it: can you, can't you, could you or couldn't you?
2) Nobody could sleep. What is the correct question tag, is it: could they or couldn't they?
Thanks in advance.