- Queen Catherine in Castle Gryphonheart - King Eldritch in Castle Navan - Judge grey in arbiter's house in harmondale

if you bring it to either Catherine or Eldritch, you'll get some gold and xp. also their country will be declared the winner of the war later and harmondale will technically be a part of their kingdoms.

If you give the trumpet to judge grey, you wont get gold, but more xp. Harmondale will become an independent kingdom.

After delivering the trumpet you'll have to wait approx 2 months, then visit harmondale town and you'll get a messenger and a new quest.