Okay, so here's what we know about your LEDs:
Forward Current - 20mA
Forward Voltage - 2.2

If you use a 9v power supply or battery and the LEDs are dropping 2.2v of that, then it means we need the resistor to drop 6.8v (9-2.2). We now know the voltage across the resistor and the current going through it (20ma or .02 amps, same as the LEDs), so we can use Ohm's law.

6.8v / .02A = 340 ohms

The next-highest standard value resistor is 390 ohms, so that's what you'd want to use (get 1/4 watt; 1/8 watt isn't big enough).