For debuging and showing a selection in the scene i currently look wich node was clicked, get the geometry from it, clone it, scale it by 1.01f, set it to wireframe mode and attach that cloned geometry to the node too.
The problem now is with quads, i can see them finde from the front side, but from the back neither the quad nor the created selectionshape is displayed.
I thought i could use a box and wrap it arround the world bounds of an object instead, but now i am at a loss on how to get those.
It is possible to get the worldbound from the geometry, but i dont see any getters on it to fetch the actual size so i can create a box that surrounds the geometry.
Am i missing something ? Or is there another way to get the bounding of a geometry ?
or you can set the face cull off on those geometries’ material and both sides will be drawn.
geom.getMaterial().getAdditionalRenderState().setFaceCullMode(RenderState.FaceCullMode.Off);
@nehon’s solution is probably the best… but to answer your original question it might have been nice to know what you tried.
For example, why doesn’t this provide the info you need:
http://hub.jmonkeyengine.org/javadoc/com/jme3/bounding/BoundingBox.html
This is when I have to start guessing that you might not know how to cast a BoundingVolume to its specific type, etc…
Haha, my bad, thanks @pspeed, wasn’t thinking about what BoundingVolume realy is, yes, with casting it to a boundingbox it works fine.
Altho i think i will go with @nehon’s solution, because that is even easier 
Only thing i wonder is if i could somehow visualize which side is the front and wich one is the back without too much fuss.
Then again i might go with an easy solution and put another quad wich indicates front side for this case.