Successfully Blackmailing or Bribing a Noble unlocks the 'Get Intel' action in your interaction dialogue. If successful, you get a report that contains which troops they have, where all their family members are located, as well as the location of all of their alliance members. Intel reports can be shared in a Private or Alliance chat.

The "Get Intel" action can be performed through your interaction dialogue with any Noble (other than your own), no matter where they're located, as long as your Nobles can reach them.