I would suggest you to go through with the given below link to check the previous year papers of JNU.

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

There is no any particulr material to prepare the exam,  There will be 100 objective type questions.

The Question paper is divided into two sections which are further divided into parts.

You will have to answer the first section which will contain objective type questions from Reasoning, English grammar, Comprehension, Language for 50 marks.

Section two will contain descriptive type questions for 50 marks

You can prefer the previous year papers to know the level of the questions.

Good Luck!