Hello Anshu hope you are doing well let me divide the answer into three parts .

Students who already has taken admission in any branch of JU. They can participate in the spot round easily. When U will go for to take spot , U need not to carry any further information like rank card, dob, bla bla bla..it's very simple procedure for them.

Students who r already admitted in a college except JU. They need to bring all the documents needed (will mention in the website's notice). But your admission charges would be higher than the JU guys ( who are already in JU); it will be 10k or something(for ju guys it's 270 or something, bhul gaya actually kitna tha :3).

Students didn't admitted any college can also apply for spot round..and the process is same for them as like 2nd category students ( those who joined a college already).

Feel free to ask me in the comment box if you are having any further doubts

hope you find it helpful 

Good Luck!