Windows 2k8 R2 - What is the UserDN belongs to 1 OU that inside the other OU?
CN=Joe Blow,OU=Office1,OU=People,DC=quang,DC=com
The CN is the common name of the user. Then from left to right, list every component in the path from where the object is all the way up the tree until you come up with a fully qualified path that leads all the way up to the root of the domain. That's the distinguished name.
Here's some more reading from Microsoft on distinguished names:
http://msdn.microsoft.com/en-us/library/windows/desktop/aa366101(v=vs.85).aspx