https://www.pcgamer.com/fortnite-lightning-bolt-locations/

Just like seasons before it, Fortnite Season 5 comes with a list of new weekly challenges to push players to do more than just murder one another. One of the opening week challenges tasks players with hunting down at least seven lightning bolts across the map. There are seventeen lightning bolts scattered from coast to coast in all, but you only need to grab seven of them. It’s worth noting that this challenge is only available to players who pick up the Fortnite Season 5 Battle Pass.

You’ll need to either fly into them or build up from nearby buildings since they are usually pretty high up. Every bolt gives off a golden glow so they are pretty easy to spot and you can collect them just like you would open a chest or llama.