And i want to scale UV Sphere depending on its position on Z axis for example. With attribute node that was done in 1 operation and now i cannot find solution, using Separate XYZ and Scale Instances in any configuration.
Four you example, just use the output of the Noise texture to drive the scale of the Instance on Points Node, since it already drives the Z location. Here's a crude version:
Since you want to keep the sphere shape, plug all the noise value into all three sockets of a Combine XYZ and use that to drive scale.
I didn't put any math in the path, but yo can add math nodes to control the range of scales.