Is it legal to write your own study and exam experience and sell it as a manuscript?

If it is a paper book, the materials should not be illegal. In other cases, it should be said that it is illegal to steal copyright.

There is also that it is illegal to sell without review.

Infringed copies specified in Article 217 of the Criminal Law, if the amount of illegal gains is huge, shall be sentenced to fixed-term imprisonment of not more than three years or criminal detention, and shall also or only be fined. Article 218 Whoever knowingly sells an infringing copy as stipulated in Article 217 of the Criminal Law for profit and is suspected of any of the following circumstances shall file a case for prosecution.