This challenge is part of Fortnite Season 4 Week 8 Challenges and you'll have to headshot Doom henchmen or Stark robots. These entities are NPC patrolling and protecting areas on Apollo Island.
Although they aren't strong, they are hostile and won't hesitate to shot at you. If an isolated target doesn't represent a real danger, once you're in a group, they may surprise you.
You have two options to complete this challenge. Doom's henchmen are roaming his stronghold in the northwest of the map while Stark robots are watching the industry in the northeast.
Map
Make sure you have the proper equipment before you get into battle as they may surprise you. These zones may be quite contested and you might come across several players.
Look for a henchman or robot and remember to aim for the head to succeed in the challenge. Owning a pistol or machine gun will help as you'll be able to deal more damage before a NPC is knocked down.
Original content by Maxime "Biaggi" Ricoveri.