There are several ways to create additional product information in WooCommerce – the most common is by creating Product Attributes, either as an Attribute taxonomy term or individually for each product, and then using those Product Attributes for variations. This is great for selectable variation attributes like Color, Size, etc., but does not work well for unique / singular information like GTIN, UPC, EAN, ISBN, and MPN (Manufacturer Part Number). What is required instead is a different way to manage this unique / singular information on the product editing page, which is then shown on the WooCommerce purchase page under the “Additional information” tab.
WooCommerce manages information on product Availability (aka Stock), Prices, SKU, etc., but additional WooCommerce product attributes must be created to provide more product information for Google.
The WPSSO Core Pro plugin (and its WPSSO Schema JSON-LD Markup Pro add-on), for example, include a variety of WooCommerce product attribute values in its Schema markup, including the product Brand, Color, Condition, EAN, GTIN-8, GTIN-12, GTIN-13, GTIN-14, ISBN, Material, MPN (aka Manufacturer Part Number), Size, and Gender.