I was trying to register my iclicker but the numbers on the back were worn off.
I even tried to find the number using the website using Mac id and student number, but no success.
Is there any other way of finding this number?

Need to find a prof with the magic box to extract said number. Titles mayyy be able to help you (by either finding the number, or exchanging your iclicker).

This happened to me last year as well. Go to Titles, tell them you need the iClicker number and they'll send you to a back room. The guy there will retrieve your number for you.

Step 1; turn iclicker over
Step 2; open battery cover using pointy object
Step 3; remove batteries
Step 4; look on the left side wall inside the battery compartment. there you will see the barcode and the number that you speak of.
Step 5; if that number has also rubbed off go to titles and ask for their assistance.

Or take off the screws, there is a backup sticker either on the inner backpanel, or on the pcb