You can refer the previous year papers to know the level of the questions. You should have the basic knowledge of the subjects like History, Economics, International Relations, Philosophy, Indian Politics. The Questions will be there from the B.A syllabus, so you need to have knowledge of the course which you have studied in Bachelors degree. 

The paper will be subjective, You can check the further information with the given below link.

https://admissions.jnu.ac.in/Prospectus/JNUEE/SIS%201.pdf

Good Luck!