UV Editor; alignment of two meshes here is a new topic I can not solve. I am using Blender 2.80.

At UV Editor I would like to align vertex from one Object to Edge of an other Object.

I tried snap incremental. But each vertex will always snap to t's own incremental mesh?
If you want to do it manually just enable edge snapping, then grab the one you want and while moving it tap X to restrict the movement to that axis alone. 
That way, you can move horizontally and snap it to the same place the vertex on the bottom is, while maintaining it's vertical position unchanged. 

All that said, I would simply add a few UV seams along those horizontal loops.