Is there a way to figure out who did what changes to a AD group using powershe

Enable AD auditing. 

Post issues about how to use ad in the Directory Services forum. They will help you with the configurations..

Need assistance in powershell. AD Auditing is enabled. 

Assistance with what exactly? If auditing is enabled, just query the log.

Unfortunately I do not have access to those DC's.  I am trying to use  Repadmin to find out.  If there is no way to figure this out using powershell + querying AD (and it attributes) , I will have to query the logs only. 

Let me dig more into this should be something in AD to figure this out. 

Access is now enabled. I have around 20DC's. Using Repadmin is it possible to find out which DC security logs I need to comb through?

Hi Priyabrata,

You need to comb security logs on all DC's on which AD object was modified.

In System Center 2012  Operations Manager, Audit Collection Services (ACS) provides a means to collect records generated by an audit policy and store them in a centralized database.

https://technet.microsoft.com/en-us/library/hh298613.aspx