Can the university teacher ask the class representative to mark the test papers and tell the roommates?

Generally speaking, if the teacher asks you to grade the test papers, you'd better not tell your roommates, because if you change the grade for him, it will definitely be particularly dangerous for the teacher, because the teacher will have to check the grades later and check the grades for other teachers. If you are very strict about correcting your roommate's grades, he will feel that you didn't help him make his grades particularly good, and if he thinks his grades are particularly poor, he will also blame you.