Q: How do I find my purchase history iPad

You can not find your complete purchase history on an iOS device. You can find it in iTunes on a computer. The best that you can do is to go th the purchased tabs of iTunes, the App Store and iBooks to see what you have purchased.

See your purchase history in the iTunes Store - Apple Support

For apps you purchased on your iPad, read this:

https://www.apple.com/support/mac/app-store/manage/

You can also log into your "Report a Problem" link to your view your iTunes purchases.