Wage reporting when hours change weekly - 7 months and counting

I picked up part-time shifts as an IT help-desk technician and I am confused about how to report them. It has been weighing on me all week. 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?

The claimant handbook has worked examples for part-time pay. Mine was clearer than the phone line.