Impress them. Learn the code yourself.

From my experience, even if the code isn't on a sticker on the product, it's printed on signage. You'll find a small four digit code, usually in the lower right area of the sign that is the product code for that item.

Almost every product at a grocery store has at least a barcode for an item on the sign, so if the product is 100% sold out, when the inventory ordering person goes around, they have a convenient way to scan the item for ordering. For regular items, it's the UPC, for produce, it can be the four digit "scan code" of that item.

This trick is also useful when stuff on the shelf is out of place and you just want to find the price, compare the barcode of the item you want to know the price of, to the barcode on the sign (usually both the scannable barcode and the digits of the barcode are printed on both), and find the right sign for the product.

This not only helps with ordering but also when the cashiers ask for a price check, the worker who is checking can confirm which product it is by its barcode, to match it with the correct item on the shelf and provide the correct price (which is why price checks can take a while). Eg. If mountain Dew is on sale but it's full price for Baja blast (only one variation of the product) they can identify that they're looking at the right price by comparing the pricing label on the shelf and its barcode with the barcode on the product to verify that this price is for this product by UPC (which should be unique by product). Sometimes it takes a minute to find the correct product pricing label for it.

Edit to add: I found this random grocery store sign (no idea what store it's from), which has all the elements you would be looking for:

The PLU is right there above the barcode and the barcode is flanked by the UPC. Where the barcode is used for ordering, and the PLU is used for the cashier to easily identify the product; usually you can also find the PLU on small stickers on the product, but not always. Just jot down the PLU and take it with you to the register.