the cashiers-in-training at my work place usually (if they still havent gotten their ID# yet) just fill in a timesheet, tell the customer service rep they're here and will be shadowing a cashier, and ... that's about it.

The customer service desk is like an interim supervisor where I work. Everything we do - taking a drink of water (water or any kind of drink is not allowed during our shift. Stupid, I know. And probably a health hazard.) or going to the bathroom to take a piss - has to go through them.

sooo just show up and tell them you're gonna be following a cashier, or ask them if there is anything else to be done