jtreg by design does not expose all environment variables to its Java children.
On windows there are certain environment variables which are critical, a test not having access to these can fail in very mysterious ways see: JDK-8248987

This is the exhaustive list of Windows 10 environment variables.
https://docs.microsoft.com/en-us/windows/deployment/usmt/usmt-recognized-environment-variables

I think inheriting the following might be sufficient for now:
{code}
CommonProgramW6432=C:\Program Files\Common Files
CommonProgramFiles(x86)=C:\Program Files (x86)\Common Files
PROGRAMFILES=C:\Program Files
ProgramFiles(x86)=C:\Program Files (x86)
ProgramData=C:\ProgramData
{code}

The values for the environment variables above are provided merely for description.

One can workaround by using this with jtreg:
    -e:NAME
        inherit env var NAME from environment

    -e:NAME=VALUE
        override env var NAME with VALUE

Use `jtreg --help -e` for more details.