A. A. The default printer is set on a per user basis and so is part of the HKEY_USERS hive. To view the default printer for the currently logged on user view the
HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows\Device
value. It is of the format "\\LN014\LN.S651.CSP001.HPLJ5,winspool,Ne01:", where the first part is the actual printer share, then the spooler and finally the connection, e.g. network or parallel port.
To view a different user or view remotely you would view HKEY_USERS\<SID of user>\Software\Microsoft\Windows NT\CurrentVersion\Windows\Device. To check which user has which SID see Q. How can I tell which User has which SID?
If no default printer is manually defined then the first printer alphabetically will be set as the default.