To be clear, you want 12V to become 0V and 14V to become 2V, is that correct?
The zener diodes I have are 12V 0.5W.
Maximum possible current 0.5W / 12 = 42mA
Maximum voltage across the resistor is 2V
2V / 0.042 = 47ohms minimum value for the resistor.
The problem is that close to 12V input there will be very little current. The exact voltage across the Zener will vary according to current through it, which will depend on the input voltage. It will also vary with temperature. How accurate do you need this to be?
I would probably use a current source through a resistor to give a fixed voltage drop across a resistor instead of a Zener.
I see this is your first post; for posting a proper schematic in you post so we don't have to download it ++Karma;