How do I calculate the power consumption of the polarity detector circuit?
You have only one voltage supply, so this will be relatively easy. Find the equivalent resistance of each branch to get the DC current through each branch, and then use V^2 / R for the power of that branch: the first example is 1.5**2/(1e6 + 5e3 + 91e3) = 2.05μW. Same for the 10M + 510k which yields 225nW. For the op-amp use its quescient current of 350nA * 1.5 = 525nW. The sum of those three is 2.8μW, the same as the stated 3μW after rounding.
If you want to be more accurate, the 91k is actually in parallel with a frequency-dependent impedance that's the combination of a 480pF capacitor and a resistance that you'd have to infer from the frequency response in the specsheet, but most likely this impedance is negligible.