how to copy one gpencil layer from one scene to another scene in the same blender file? how to copy one gpencil layer from one scene to another scene in the same nlender file ?
Try this:

In 3d-view change mode to Edit Strokes:



Then select strokes (for example using A, C or B), then Ctrl+C.

Then move to different scene  create a new layer, set mode to  Edit Strokes and press Ctrl+V.