Where do i find magical girl nursery rhyme?

In the candy land I believe, just follow the "next" sign in the overworld and you'll be fine

She is in the Candy Castle level, you have to beat her a few times to fully clear her mission and get the ticket.

It's a multi-stage fight. To unlock additional stages, there's usually a specific mission you need to complete, often by doing the other nodes that are around the castle. Follow the guide here on the site, it'll get you through without using up too much AP.

i really reccommend using this sits event walkthrough. itll make sure you clear it in an ap efficent manner