I go to university twice a week and the university is 3 hours far away from my house. I have to miss namaz fajr because of train sometimes, there is no space to pray there.
Namaz zuhr & asr I pray there. My question is, do i have to do qasr for namaz fajr, zuhr and asr? Or qadha for fajr and pray zuhr and asr regularly

Pray your zuhr and asr as normal. As for your fajr namaz, don't do qadha if it and try to pray it in whatever manner you can even if it be while standing and with gestures. And try and maintain the qibla to whatever extent possible.