In order to find portal web adapor, you must first find portal admin directory
Then portal web adaptor is right here
But where is my portal admin directory
In order to access your portal admin directory, first you need to find your portal home
For example my portal home is
https://gis1.victorvilleca.gov/portal/home
Then you will change URL,
/portal/home
to
/portal/portaladmin
Then this is your portal admin URL,
https://gis1.victorvilleca.gov/portal/portaladmin/
you can access portal admin through portal web adaptor, this is biggest difference when compare to arcgis server admin directory and arcgis server manager. To access arcgis server admin and manager, you can not through web adaptor, you must direct access arcgis server install machine with seure port 6443.
Now Login as portal admin