Mostly IIMs have replaced group discussions with a Written Ability Test (WAT) to make their selection procedure more efficient.
As a debate on this decision could run for a day long, it is important to understand what they look for from a candidate in these written tests so that you can figure out a few topics and practice.
The topics for Group discussions can also remain the same as only the format you present your information differs from a written test that is verbal. As a matter of fact, GD is not being completely overhauled by all the IIMs altogether.
The following are the possible broad categories that you can expect a topic be given to write on.
One example question on each category would be as mentioned below: