i got campus placement last year, and in my opinion, the reading you will do on any given issue will be irrelevant because you cannot predict what they will ask. You will anyway be given 10 mins and possibly a pen and paper to write down your thoughts on the topic before beginning.

WHAT is more important is that in a GD, people are literally pouncing on each other to speak. Remember, everybody wants a job, they're all your competitors and they have no incentive or willingness to let you speak as everyone is looking to get their own words in. So what you do need to work on is HOW to spot and overtake the final statements of one person's speech and then make your own points without interrupting or being loud. The smooth transition-by-overtaking is by far the most important thing in a GD like this. I am speaking from personal experience because I failed to recognize and capitalise on moments where I (or any other GD participant) needed to take over from the speaker, and thus regardless of my knowledge I was unable to convey my points, and I did not make it to the next round.

I learnt from my mistakes and was far more proactive in the next GD the following day, where I made it to the interview round.

The mic is literally 2 pounds of meat between 15 hungry lions. Keep this in mind, always. Nobody will give you a chance, you have to take it.