No one knows! That's kind of the point. We know some of the fundamental limits and constraints of what goes on around and inside a neutron star, but the essence of it is still a giant mystery. We'd have to go and look, and that's not likely to happen any time in the next ten thousand years or so.

Oh ok, but what in our current understanding could let us suppose this difference in sensing? And by hemispherical do you mean somekind of fisheye projection? I would really like some beginner ressource on this subject.

A dolphin is surrounded by water, and its sonar sense is truly 3D, in that it can go in any direction. Up, down, left, right, ahead, or behind.

A creature living on a neutron star might use sonar like we do light, because the speed of sound in the star crust is more then half the speed of light. In many ways it would be comparable. But the crust is only below the creature, not above. So its "sound sense" would only work for one hemisphere surround the creature, the other side would be silence, its equivalent of total darkness.

Neutron stars have thin crusts, possibly mere meters thick, and almost certainly with layers of some sort. Again, sound would probably travel at different speeds in the various layers, just like sonar does in oceans, where salinity affects propagation. There would be complex effects with distance to do with this. Locally, the sound could travel outwards in a hemisphere, but at long range it would likely be more 2D.

This is all speculation, but it's based on real science. My point is that we cannot really know, and no amount of staring at equations will help paint a realistic picture.

Oh so I guess that At long distance it would behave like a map splatted on a sphere? Still hard to wrap my head around, but it is cool stuff!