Managers are citizens which provide certain bonuses to buildings once they are hired.
There are three Research options related to managers and researching all three greatly increases your available managers.
FOREMAN - Unlocks managers for production buildings
GENERALS - Unlocks managers for Military buildings
EXECUTIVES - Unlocks managers for entertainment buildings
The key to unlocking this achievement is too grow your population, advance into the modern era. As soon as its available pay £10,000 for the Census edict, this will identify all skilled citizens.
Like most of the achievements in this game this will come by being patient.
Select any building press down on D PAD and press Y to hire manager. You will now be shown a list of all of your available managers. To unlock simply assign 15.