The best thing to do is to run a Detailed Device Report for the device in question, and find the section which contains the information you want. For example, if you're looking for module part numbers, the module section is what you want. You can use this as a way of understanding what each Inventory Group can provide.
I think you'll want a custom report template like the following to get just about all possible part numbers:
Module:Vendor Type
AND:Chassis:Chassis Model Name
AND:Chassis:Chassis Vendor Type
AND:Processor:Model Name
AND:Processor:Vendor Type
AND:Asset:Orderable Part Number
AND:Module:Model Name
