You have two choices - supply your own GUID in the metadata, and this overrides the randomly assigned one, or look in RDP/ssh for it (which is more work than needed - highly recommended you add your own GUID, this way it doesn't need to be copied or grabbed from RDP/ssg)
wmic PROCESS get Caption,CommandLine | FIND "GUID"
but write the results to a txt file on the desktop. So...
wmic PROCESS get Caption,CommandLine | FIND "GUID" > Desktop\t.txt
I don't know why OTOY would NOT have put that value in the instance metadata on startup???