Based on the planet from this question. The main thing that distinguishes this planet from, say, Europa, is the handwavium light-source, which I must assume is wrapped in a perpetual explosion wrapped in strong currents, due to the extreme temperature difference. How extreme this would be varies as things stabilize, so let's say we're talking after things have settled down as much as they will.
Intelligent creatures on this planet would probably be able to estimate their distance from the light-source, even if they can't see it (would they even evolve vision, since the light only goes so far through the water. The currents will have predictable directions for quite a distance, so relative positions aren't too hard.
But is there a way to determine something analogous to lattitude and longitude? The planet has at least one satellite. I'm not sure if it would have a magnetic field separate from the handwavium (if it does, that seems like it could solve the problem).
Since they have the light-source as a reference point, just one of lattitude or longitude should be sufficient. Ex, if they can tell that they are so far north or south of the LS, the rest is simple geometry.
Alternatively, if there is an established theta = 0, they can just use polar coordinates, with the LS as the origin. But is there a natural way to establish theta = 0, and identify where one is relative to it?
If it makes a difference, I imagine the LS being north of the equator, though how far is not firmly established.