If I have multiple Druid of Horns on the battlefield and cast an Aura targeting one of them, will each Druid trigger and create multiple 3/3 tokens, or will only one token be made by the Druid being targeted?
Only the druid targeted triggers. When a card uses its name it actually means "this card" when they want to effect all cards named the same they use "cards named X".
Multiple Druid of Horns