How do you report hours that vary week to week?, dental hygienist here

My hours change every week at my new part-time job and I am afraid of reporting wrongly. It has been a long 5 weeks. 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.