I had given the interview for a summer internship in CAT. I was just at the end of my 2nd year of engineering and had to give my interview during my semester end exams ( It's on college for that one ) Now coming to the interview, it went for about 45 mins and was mostly technical questions. Fluid mechanics, thermodynamics, IC Engines, basics of automobile and SOM, TOM etc. From my experience they weren't looking for a genius but simply for someone who's willing to learn, confident, curious, problem solver and has a brain of their own to question anything in the first place. Apart from that, Hands on learning through extra curriculars will be appreciated as well. But i'm telling you guys, Text books are your friends.