How do you see history of ACL, who changed what & when?

Hi Sreedhar, there is no built-in history on the ACL objects themselves but you are on the right path with using the Audit Log. To see this, you would need to enable logging of the "Integrity Server" types of activities which will include changes to ACLs. For example, un-comment this line in the is.properties file:
     mksis.auditor.is=true

Note: A service restart is necessary for any changes to the properties files to take effect. Then going forward you will see entries in the audit log similar to these whenever a user makes changes:

Hello Sreedhar Chinnaswamy,

If you still need assistance with this, can you please let us know the challenge(s) you are still facing?

It looks like Joe's solution is correct, would you please take the next step and mark this answer as "Correct Answer"?

This way other users reading the thread will know there is a solution, and which answer is correct. In addition, it makes the solution easier to find.

Thank you,

Adam