merge form variables for standard fields

Where can I find the variable names for fields that aren't displayed on User Defined Forms? I'm trying to add standard fields that are found in the Structure block (Primary Location, Org Name, etc), for example, to a merge form as shown in the image below. However, there's no corresponding User Defined Form to source the Binding Field naming convention as suggested in the discussion linked below. I'm recreating the PDF that's delivered when you view a req in Recruiting and hit the Print button to create a PDF, i.e., all the fields on the Requisition File so I'm also