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):
LD 20
REQ prt
TYPE dnb
CUST (usaully zero unless tenanted switch)
DN <cr>

This will print all DNs in use on the system.

To see what RPNG an extension belongs to:
LD 11
REQ prt
TYPE dnb
CUST (usaully zero unless tenanted)
DN xxx (where xxxx is the DN (extension))
<cr>
<cr>
<cr>
<cr>
Write down the PORT Number

REQ PRT
TYPE TNB
TN ## ## enter the PORT Number you just wrote down
WATCH for RNPG Number (Ringing Number Pickup Group)

I hope this helps.