Easiest way is to have a texture as a height-map/displacement-map. Then use this: How2Displacement - Album on Imgur
But plug it into World Position Offset & ignore the tessellation multiplier.
Bump-offset works by taking in a heightmap and mucking with the UV’s based on your vector to the pixel. Either way you still need some kind of height information.
WPO would be preferred in that it’s actual mesh alteration so it could (more) correctly impact lighting by simple virtue of it’s position. The math there kind of comes out in the wash.