JNU has different schools of subject which offer courses in Political Science they are as follows.

1. School of social sciences further has a centre of political studies which provides an M.A. in the same. This is the link to the programme; https://www.jnu.ac.in/sss/cps-MA

2. Another school is School of International Studies which can be opted, there are further many centres of studies under this school. This the link to the same; https://www.jnu.ac.in/sis

I recommend you to go through the links and options that JNU offers and discover for yourself a course which interests and suits your needs. 

Regarding how to get an admission in JNU for masters please check the eligibility criteria for the courses through this link https://university.careers360.com/articles/jnu-eligibility-criteria

The admission forms for 2018-19 have already been closed. JNU admission 2019 will be start from the month of September'2018, I request you to keep a lookout for the forms and entrance exam dates on the official website; jnu.ac.in