Hello @johannaox,
Thank you for posting here in the Community. I'm here to help you set up SKUs in QuickBooks Desktop.
Currently, a specific field for SKU is unavailable. As a workaround, create a custom field for the additional details in the item information.
Here's how:
- Click the List tab at the top menu bar.
- Select Item List.
- Press New.
- Click Custom Fields.
- Add a new one.

- Hit OK.
I've attached the following article that can help you with updating item information in QuickBooks: Add, edit, and delete items.
Please let me know if you need anything else regarding managing inventory in the Desktop version. The Community and I will be here to help you.