In the Adventures in Middle-earth Audience rules, after the starting attitude has been established by an Intelligence (Traditions) check and comparing the cultures on the Starting Attitudes table, the players may make a request of those they have sought an audience with. The Reaction DC for that request is determined by the starting attitude, but no ability check is listed. Is this intended to be a raw die roll? Seems to me like Charisma (Persuasion) would be appropriate, but this is not mentioned.
The text does not mention any reference to the DMG's Social Encounters, but the format is identical to the Conversation Reaction table on page 245, making it seem as if it was intended to be Charisma, either Persuasion, Deception, or Intimidation.