The 'Blackmail' action unlocks on any Noble that has the 'Ashamed' trait, a trait that is applied when they are 'Boinked' and have a child out of wedlock. A successful 'Blackmail' unlocks the 'Get Intel' and 'Open Gates' actions.

Blackmail is available to the Noble that did the 'Boinking' for a short period of time after the 'act'. The option can be found in the interaction dialogue between the Nobles in question.