回複：向誰申請？

Your understanding isnot correct. I-9 is just for verifying eligibility purpose, but not for employment authorization. As far as I know, if you apply for a part-time on campus job, you could do it through your school official (for detailed info, please check with your school's international student service). As to off-campus job or full-time (not a summer job), you should use I-765 to apply for authorization.