The product codes for Esri products can be found in the following online documents:
If the product code is not documented online, for example, when the product is new, the code can be found in the Setup.ini configuration file of the product's installation folder. To locate this file, follow these steps:
The product code is displayed in the ProductCode line found in the Setup.ini file as shown in the image below.
ArcGIS Pro does not have the Setup.ini file within the installation folder. Instead, the product code is available in the 03ws00000008000000 HTML document located in the following directory:
C:\Users\<Username>\Documents\ArcGIS Pro 2.x\ArcGISPro\Documentation