Hii Kanhaiya!
You can get the model question paper of BSEB for the Maithili subject on various online portals. They are available in the form of PDFs too. You can even get model question papers or sample papers in Youtube tutorial vedios. They provide question papers as well as their solutions in the same vedio. BSEB official website will also help you in finding the sample papers. Hope this helps.
Good luck!