Which subjects can I choose to pursue Masters after completing B.Tech in CSE?

I think you should complete Masters in computer science as you have completed post graduation in computer science then you are more experienced in this field than any other candidate. So, my opinion is to do your Masters in computer science. Thanks.

There are various subjects in which you can do the Masters and this mainly depends upon the university/institution you are taking admission in like there are special streams/subjects that only a particular college is offering and none other than that is offering that degree/specialisation.