What will you do when you discover a violation of the law on religious beliefs?

Depends on what the law is and what the violation is. If it is a disagreement on principle, I would do nothing. People are entitled to differing opinions.

If it is the burning of a church, that is an entirely different matter. Property destruction is never legal no matter what the destruction is about. Because you hate minority groups does not give you any right to destroy what is theirs if they have paid for it.