The History tab of the Apply Catalog Updates menu item will indicate all the changes that have been made in your IQS database.
The first column of the History table indicates the type of change that occurred, Add, Update or Delete.
The second column indicates the reference data table where the change occurred.
The third column describes item (e.g. specific course name, job title etc.) the change was applied to.
The fourth column indicates the type of update that was applied.