How can I verify, test and/or reset my Domain Join (aka SecureChannel) from the endpoint to domain controller?

You can use PPUPDATE to show the current domain joined status.

Here is an example of PPUPDATE command showing a correctly joined on-prem Active Directory joined machine:

When not domain joined:

When the secure channel has been broken and needs to be re-established:

See this Microsoft article on Resetting computer accounts in Windows for additional information.

To attempt to reset the secure channel on a specific PC, make sure you have network connectivity to a Domain Controller.

Step 1 – Open PowerShell As Administrator:

Test-ComputerSecureChannel -Verbose

If False then run:

Test-ComputerSecureChannel -Repair -Server PDCEmulatorName -Verbose

If repaired you will see message, if it fails then try adding a credential:

Test-ComputerSecureChannel -Repair -Server PDCEmulatorName -Credential Domain\UserName -Verbose

See this article from PCPMag, Rejoin a Computer from a Domain In One Easy Step! for information on alternate steps.