Which resistor watt rating to use for this circuit and Arduino 5V?
If your situation is the same as that of the author of the article, the power dissipation of the resistor is (5-4.096)^2/560= 1.5mW. Any resistor you can buy is capable of that (the lowest I know of are rated at 20mW (0.3x0.15mm).

You can use higher rated resistors.. Any leaded or chip resistor will do. The tolerance is not important in this case, it is the LM4040 that determines the reference voltage, and it changes little with current.