Dear Student,
If your marksheet is lost then you need to apply for duplicate marksheet with following documents.
1) Affidavit on 20 rs. stamp paper with all your details (name, address, Enrollment no, college name etc) and also about lost marksheet details.(Also mention that if you got original marksheet then you will submit the duplicate copy to the university back in the affidavit).
2) Receipt of fees payment in category of "DUPLICATE GRADE SHEET" (Per marksheet 100 rs.)
3) Net copy of lost marksheet (or if it is not available then attach the "Student Grade History" and highlight the marksheet which is to be print).
Download the application form from above link, fill up it, attach all the required documents mentioned as above and then submit it at GTU, chandkheda, and keep one copy with you of all documents for your reference.
thanks.