Mock seat allocation involves entering your preferences based on which they predict what college you can get. After entering the preferred options as per them candidate get fair idea what they can expect. It is somewhat a prediction what you will get in the 1st round of counseling. 

Hello Anurag, 

Comedk mock allotment is quite similar to a JoSAA allotment. It is the process by which you are given an idea and a seat is allotted to you based on your preferences. It makes use of the information about the preferences of the others who had entered before you and allots seats based on the fact if the others do not change their preferences. You can then get a fair idea of your seat availability and choose accordingly. 

I hope this helped.

All the best!!