For JNU you can get the previous year question papers from the link below:

https://admissions.jnu.ac.in/searchquestionpaper.aspx

For BHU you can get the previous year question papers from the link below:

http://bhuonline.in/old-qus-paper-entr.html

For DSE & JMI there are no specific official website for download nor any perfect book.

For JMI or DSE I would recommend you to search on Google or just contact your seniors who had prepared for this for previous year question papers.

I hope this answer helps. All the very best for your future endeavors!