how to detect the enforced gpo

my quess would be: you need to audit the target box to where the source DC pushes GPO to.

I'm with Aidar on this one - if you want to see the details of what was applied, you need to audit the end point. The changes are manifest as Registry modifications I believe.

The only thing you will typically see on the DC side is that fact that the DC's computer account(s) is (are) doing stuff related to GPOs and then (I think) only if those GPOs are applicable to DCs.

So, in a nutshell start by looking at activity by the DC computer accounts. Then, as noted, you will likely have to consider auditing the end point.

FWIW, PoSh calls to the WINRM service on the end point can tell you what settings were GPO applied. Try:

winrm get winrm/config

This will show you what settings were applied via GPO.