Items can be looked up via SKU by using the keyboard on the device or by using a compatible barcode scanner. Enabling this feature can be done by Navigating to Device Setup.
Then, enable SKUs under the Order Screen section.
From your device, you can assign menu items a SKU number by accessing the item in quick edit mode and scanning or entering the number into the SKU field.
Once the item has been published, you can scan or manually enter the assigned SKU into the search field at the top right of your screen. It will be added as a line item to the new or existing check.