Where is the "new" document stored on disk WP2020

You can indeed view where the template resides.

That does not answer the query.

Confusion may arise because if the user chooses to create a new WP file from Windows - in Explorer Rclick>New... - then there is an actual file that Windows uses.

You do understand that when WordPerfect starts up, it reads the general template and creates the NEW document as well as temporary files.  In the case of 2020 it reads the template WP20US.WPT which formats ANY NEW document. 

I am not sure if you understand how operating systems and applications work in conjunction with one another.  WP starts up and makes a request to the OS to locate particular files that WP needs to perform it's duties.  WP is the driving force but does make requests for particular Windows system functions.

If a general user like yourself wants to view what folders, files, etc. are open by a process (like WP) you can go to sysinternals.com and download the process explorer application that is free.

You execute process explorer and locate the WP process it will list everything that is open by WP at that moment.

> You do understand that when WordPerfect starts up, it reads the general template and creates the NEW document as well as temporary files.  In the case of 2020 it reads the template WP20US.WPT which formats ANY NEW document. 

Yes. And WP20US.WPT is not

> the wpd file from which that new blank document was created

straight from WP

The default template is applied each time you open WordPerfect or click File } New. By default, WordPerfect installs and uses a straightforward workspace template (for example, wp20US.wpt) as your default template

I find in WP Help:
When you open WordPerfect, the blank document you see is based on the default template—a special WordPerfect template (WPT) file that records various workspace settings.
Besides storing basic document settings (such as the default font and the default text and graphics styles), the default template also stores any customizations you make to the WordPerfect work area.