Where would the red navigation light be located on a power boat?

The most typical and obvious answer is on the Port (Left) side of the vessel. However there are more red lights dealing with the navigational lights on a vessel. Depending on the location and placement they could be lights for a vessel not under command, a vessel constrained by her draft and a vessel aground. A pilot boat and a sailing vesselwill display red lights in a different fashion.

Rules 25,26,27,28,29 & 30 are helpful.

In order to learn more refer to in the 1972 International Convention for Preventing Collisions at Sea (72COLREGS or Rules of the Road) link provided below.