The trick is to get both paths on the same path 'layer'. You can do this with a simple copy and paste. Then in the that layer select both path components with the path selection tool. This will allow you to access the tool bar with the combine modes and buttons (see attached). You'll only see this tool bar when the path selection tool is active.
Thanks this works nice!
Now I am trying to move the layer content, and the path(part) that belongs to that layer
at the same time, to the right position.
Did not succeed so far, can only move the path or the layer.