Using Audit Trail Manager
The Audit Trail Manager (accessed by navigating to Tools > Audit Trail Manager) allows a system administrator to view all of the changes that have been made in K2. The results are returned in a grid so that the module, user, date, field, old and new value can be filtered.

The K2_WorkflowRefreshCache workflow needs to be installed and running to return results.
The date period for returning records defaults to the past month but the date range can be edited.