Kenat,
Just had a look at this and there is no way to get at the layers of a part or sub-assembly while you are in the parent assembly.
What you can do, however, is create sketches on different layers in the parent assembly, or different parts of a sketch and then show and hide those layers.
So you can only show/hide layers in the active file.
Not much use really because you could just create different sketches.
bc.
2.4GHz Core2 Quad, 4GB RAM,
Quadro FX4600.
Where would we be without sat-nav?