From my research top contenders are
Amethyst from Steven Universe on account of her actually twerking on screen
Flame Princess from Adventure Time due to her Big Booty and Rap Career, it would make perfect sense if she had some Twerking Skills.
Cake the Cat also from Adventure time has complete control over her body and can shapeshift ass cheeks so Twerking would be easy for her.
Miko Kubota definitely is athletic and has the ass for it, being a smug teen raises the likelyhood of her twerking as well.