..was looking for UserName from SessionID so I put this together
#include <Debug.au3> ; for _DebugArrayDisplay()
; all you can get from _WTSQuerySessionInformation()
Global $i = _WTSQuerySessionInformation(-1, 4) ; current user's SessionId
Global $__a_WTS_INFO_CLASS = StringSplit("WTSInitialProgram,WTSApplicationName,WTSWorkingDirectory,WTSOEMId,WTSSessionId,WTSUserName," & _
"WTSWinStationName,WTSDomainName,WTSConnectState,WTSClientBuildNumber,WTSCli