Question

how to write bonafied application to school​

Answer 1

Actually you don't write bona-fide certificate to school..

It is the school which issues the bona-fide certificate to you

Is it the formal letter asking the school for issuing a bona-fide certificate? If so you can simply state the reason for the same.

Eg. I want it because a particular institution needs it or any other reason

Hope this helps..