I want to ask what book or paper I wrote with, and it won't be printed on the back.

Ordinary A4 paper will do. If you want to practice calligraphy, there are ready-made calligraphy art papers. There are many supermarkets in Tian Zige or Mi Zige. If you want a notebook, you'd better buy a notebook with the inside pages of Taoist paper, which is the inside pages of offset printing paper. Of course, if you want to use bulk paper, you can also buy A4 Taoist paper online, but it is more expensive, and writing with a pen will be very comfortable.