This very simple double hook will allow you to hang something on the edge of anything that has a rectangular profile:

• the top edge of a cabinet door
• a shower glass door
   

Hooks are between the things I've printed the most because they are easy to print and always useful around the house. 

I've made an almost identical hook previously but this time I needed a smaller version of it to hang my Bluetooth speaker on the glass door of my shower (I know first world problem..)
I've decided to remodel my previous version to be completely parametric and easy to modify customize for other needs.

The model can be opened with FreeCAD and the parameters can be customized in the spreadsheet.