Is it easy to get US green card if you study at a top uni?
I don’t think getting a green card is related to studying at a top uni - unless you count the fact that at a top uni you meet smarter people of the opposite sex which gives you more chance of falling in love with an American and getting married, thereby securing you a green card. That’s probably the easiest way of getting a green card.
The first step of getting a green card the traditional way is like Louisa said - you need to get a job first. And for certain jobs, studying at a top Uni definitely helps. After receiving a job offer, you can be in the lottery for a work visa. After working for a few years then you can apply for a green card. There are many variables at play here, so getting a green card is a long journey, no matter which university you go to. Of course there are some exceptions to the rule.