CITROËN DS 4 Handbook page 238

For BlueHdi diesel versions
If your vehicle has an electric parking brake,
the jack is stowed in a bag placed in the boot.
If your vehicle has a manual parking brake,
the jack is stowed under the spare wheel and
under the storage box:
F remove the "space-saver" type spare
wheel,
F remove the polystyrene storage box,
F push the jack forward, then lift it by its rear
part.