The License key number for Plesk can be found at Server -> License Management page in the Panel administrator Control Panel. Find "Key number" field.

To get the Key from shell

1. Parallels Panel 7.x - 8.x:
# grep 'Key number' /etc/psa/psa.key

2. Parallels Panel 9.x:
grep 'key-number' /etc/sw/keys/keys/key*


Plesk for Windows:

1. In Plesk control panel go to Server, License Management and see the license number there.
2. Use the command in the command prompt:
"%plesk_bin%\keymng.exe" --get-key-number