Question : wsus

Is there anyway to enumerate which wsus server my PC is downloading the security updates from?

Also, is it possible for wsus to patch servers in different domains?

Answer : wsus

You can check which server you are using by scanning through the %windir%\WindowsUpdate.log

You should find a line that is along the lines of:
Server URL = http://wsusservername/SimpleAuthWebService/SimpleAuth.asmx

You can use WSUS to patch servers in a different domain, as long as the remote server can connect to the WSUS server then it will work. WSUS is not tightly integrated to AD.