https://www.gamespot.com/articles/fortnite-where-to-find-jigsaw-puzzle-piece-locatio/1100-6461734/

Fortnite Season 5, Week 10's challenges are now live--the final ones of this season, and the clock is ticking to get them done. We've already detailed what the week involves, including how to complete the Search Between Covered Bridge, Waterfall, and 9th Green challenge in the paid Battle Pass tier. However, in the free section there's also one challenge that requires a bit of legwork, which we've already done to save you some time and effort in tracking down the key locations.

The Search Jigsaw Puzzle Pieces in Basements challenge is pretty self-explanatory in terms of your goal.. But given that the very large Fortnite island has quite a few basements for developer Epic Games to hide jigsaw puzzle pieces in, a little guidance can go a long way in tracking down where you have to go.