PPN (Publisher Part Number) also called SKU or Manufacturer Part number in some other cases, is the unique identifier of a software model, usually attached to every purchase order line to clearly identify which software or package is purchased by a customer.
If the software is purchased through a distributor/vendor, the vendor may have a different code but the customer should be able to ask the vendor to provide the PPN as well.
There is a content team from ServiceNow who is maintaining the lookup table (Software Asset Management Content Service (servicenow.com)). There is a scheduled job to update that table on a weekly basis once you opted into the content service. Steps can be found here - Enable the Software Asset Management content service | ServiceNow Docs
Like Mike Condon mentioned, you have two options to create the entitlement. Else, in case you don't have all the details (like DMAP, license metrics etc.), another thing you may want try is to raise this part number to HI support who can then work with the content team and see if they can find the details. But this approach will usually take a few weeks for ServiceNow's team to verify the part number and add it to the content library.
