get UV coordinates on world position in fragment shader

in my project i want to simulate 2D bevel in shader so i need UV coordinates of texture on another world position (the imaginary light source)

i need to convert this vector:

 float2 offset = float2(_FakeLightPosition.x-IN.posWorld.x, _FakeLightPosition.y-IN.posWorld.y);

to difference is between UV at _FakeLightPosition and IN.posWorld on the same sprite (texture)