Where are the Bifrost Marks in Fortnite?
First of all, it is important to note that you must imperatively be equipped with the thor outfit, which is unlocked at level 1 of the Battle Pass and the challenges from level 15. Once done, you will have to take the direction of the Authority, to go a little further south (see the map below ), in order to find Bifrost brands, next to a wooden cabin northeast of Weeping Woods. They are not very complicated and are visible from quite a distance.Once there, you just have to walk next to them to complete the challenge. When you have reached level 15 and completed the other challenges, you will unlock the God of Thunder emote.
All Awakening Challenges for Thor can be found here.