Hello himanshu!

If you want sainik School practice papers for class 8 you can go to Sainik school question paper (https://sainikschoolkalibangan.com/downloads/) . After opening the link you will  get a page with options to select your class. You must select class 8 and then click on download.

This way you will be able to access practice papers using your email id.

Best of luck for your preparation!