IdentificationNumber

You are correct, but you should be able to use the defined relationship between Employee and EmployeeIdentificationNumber. I took a quick look and found these three fields:
- EmployeeIdNumberCountryRel.IdentificationNumber (US format 999999999)
- EmployeeIdNumberCountryRel.IdentificationNumberDisplay (format based on country - US format is 999-99-9999)
- EmployeeIdNumberCountryRel.PartOfIdentificationNumber (format 9999 - note that this is NOT the last 4 - is is four digits from different parts of the ID Number)

The most reliable way to find these is to go to the grid related to that page and use the Personalize function. This will let you browse the available fields for that BusClass (real, derived, user, etc) as well as all the relationships for that BusClass. If you can successfully add the field to the grid, then you should be able to add it to the page via config console.

By the way - you should be sure you consider security as well, since that screen can be seen by anyone who has view rights to that employee. For example, there probably isn't any reason for a manager to have access to their subordinates ID numbers. In our company, almost nobody has access to the EmployeeIDNumber other than the HR folks who are responsible for doing the data entry and the employees themselves.

Good Luck.