Hello Student,

Sorry to say you but actually you have not mentioned about which examination you are talking about that so it is quite impossible to tell about all kinds of examinations here. However if you are talking about any online examination there maybe some kinds of mails or messages in your phone. From there you can easily check your your roll numbers. You also can check out your files and folders whether if you have any hard copy or soft copy of the admit cards. All the way if you did not get your roll number for some online official examinations there is some and other options to recover your roll number as well. And if you're talking about your college roll number then you can easily ask your friends about that or can direct contact to the college authority for the same. Hope this will help you