Hi!
Should I create different UHD cache file for each render resoulution or I may use one, created for biggest size?
Each of this green points for GI pass corresond and linked to 2d screen space or to surface of 3d objects?
You can use it for any resolution. It contains samples in world space (or in your words: it corresponds to the 3D surface), but it is indeed smart to create from the biggest size, as sample count is determined from resolution, as well as the more hidden "precision" setting.
The green points are where UHD cache will
NOT be used, but instead will switch to path tracing.
This is the case, where the Bounce information is of no use, as in surfaces without diffuse component or purely direct light.
