Wage reporting when hours change weekly, accounts payable clerk here

I picked up part-time shifts as an accounts payable clerk and I am confused about how to report them. I have read a lot of threads here and could not find my exact situation. The form asks for gross earnings, which I do not see until later. Do you report when you earned it or when you were paid?

Report honestly and keep your stubs. An honest small error is much easier to fix than a missing report.