Is it possible to access to this contours via Robofab (for example launching a script from Terminal) in some way?

I can't find documentation about layers in the Robofab website.

Thanks

you can find the RoboFont add ons for robofab API docs here: http://doc.robofont.com/api/robofab-extras/

to get access to your layers data:

# get the current glyph from the current layer
glyph = CurrentGlyph()

# get a layer
layerGlyph = glyph.getLayer("background")
# if the layer doesn't exist it will create one

This API is only available in RoboFont. The UFO3 robofab will be able to handle layer data in NoneLab.

Otherwise you can install the RoboFont shell script that allows you to execute scripts in RoboFont.
see the Extensions > Shell tab in the preferences http://doc.robofont.com/documentation/workspace/preferences/extensions/

good luck