QHow does this follower's ability work?

AEach opponent who has a follower with the highest attack among all followers on the field deals 4 damage to their own leader.

For example, if the highest attack value among the followers on the field is 3, and one of your opponents has a 3-attack follower on their field, their leader takes 4 damage. If 2 of your opponents each have a 3-attack follower on their field, their leaders each take 4 damage. If you have the only 3-attack follower on the field in this case, then nothing happens.