What should be the exit criteria for a EPIC OR when can we say that an EPIC is complete?

[Nic Brough -Adaptavist-]

When all the stories are done.

[Mike Burns]

Unless those stories are no longer valuable. The epic might be done but the remaining stories are no longer valuable but we'll keep them around just in case we need to refer to them later on. Of course jira allows for these to be "closed" or "no longer required" resolved value as well as a done state which is not "done done", but that can be difficult to understand. 

The coaching answer is "it depends" - cause it does. It depends on what done means to your team and product owner.

Write your DoD in confluence and use it - unfortunately Jira does not allow for exit criteria to be written at the top of each column on the kanban board so you need to refer to the DoD somewhere else.