Quick guide to show how NPC zones work and what you need to do to make it work.
First place the Employee floor.
Setup a room with a door.
Place a Employee zone it must touch the door.
If the Employee zone does not touch the door or there is no door Normal NPC can walk in and Employees can walk out.
This also works for Metal Detector.
If you want you can add a AI Employee Interest Point you can add it anywhere in the room, it just a point where the Employee NPC go more often.
NPC Kitchen Staff
Place a floor with a NPC Kitchen Staff (the model of the Kitch Staff will look like an Employee but in game it will be the Kitchen Staff).
Make a room with a door like the room for the Employees NPC only that you add a Kitchen zone instead of the Employee zone.
As with the Employee zone, the zone must touch the door.
Just place them where you want except in the Employee area and in the kitchen area.