It’s the same as the older Meridian 1 series as far as I am aware and I used to work on those so here goes, it has been a while for me though :S
To Show Directory Number Block (contains all DNs in use on the system):
CUST (usaully zero unless tenanted switch)
This will print all DNs in use on the system.
To see what RPNG an extension belongs to:
CUST (usaully zero unless tenanted)
DN xxx (where xxxx is the DN (extension))
Write down the PORT Number
TN ## ## enter the PORT Number you just wrote down
WATCH for RNPG Number (Ringing Number Pickup Group)
I hope this helps.