in Call Manager 7.1.5,
if you know what the Call Pickup group is, then you go into Call Routing > Call Pickup, search for the pickup group. Once in the page of the pickup group, drop down on top right and choose dependency records. This will show you the associated DNs.
If you do not know the pickup group, but happen to know one member, then,
go to Call routing > directory number, search for the number and go into its page.
On top right, choose dependency records and click on the pickup group (popup window).
Go back to the main page, when it has now changed to pickup page.
Then again, top right > dependency records..
Hope this helps.