Jojocore is a 2020s aesthetic based around the manga/anime Jojo's Bizarre Adventure. Themes of Jojocore include flamboyant fashion, bright colors, lots of makeup, similar to the characters from the anime. In short, it's Animecore on all sorts of steroids and HGH while partaking in a really strict workout regimen.
Fashion is about colorful flamboyance like at a model show. Think very bright prints, colorful hair, and lots of accessories.
Music is a big part of Jojocore. Recommended music would be bands/artists referenced in Jojo's (for example, Prince or King Crimson), but older music as a whole is very Jojocore (however, newer music like Snoop Dog or Rhianna are also Jojocore)