Hello Sanjukta,

There is no paticular book for the prepartion, You can prefer your Post Graduation syllabus to crack the exam. You will be examined in Literature in English, Literature in India and Other Parts of the World, English in India, Literary and Cultural Theories, NonLiterary Artistic Forms, and the Relationship between Literature, Culture and Society. The objective of the test would be to specifically assess the research aptitude of the candidates, and their suitability for a rigorous research programme.

You can also prefer the below given link for the further information.

https://jnu.ac.in/admission/e-prospectus-2019-20.pdf

Good Luck!