This is an advanced task:

Enable the FileView in Marble (Settings->Panel->File View).

You can browse through all the files that have been opened to display the content in Marble.

If you browse through the tree hierarchy you can see that some elements there are "GeoDataPlacemarks". There is currently no option to introspect the detailed properties of such a placemark.

Please add an RMB menu. The Menu should only appear for GeoDataPlacemarks.

Initially it should just contain a single menu entry: "View Properties"

Clicking the menu entry should launch the EditPlacemarkDialog that is used in the Edit Map panel and Tour panel already (you might want to look into their source code as an example).

The required data should appear in the dialog

Since we don't know about write access we just display the dialog in a state where all controls except for the OK button are set disabled so that the user can not modify values.