Hi,
as the error says the dce-wifi-ccnx example is not there. Please *read and understand* the output and the documentation. The available example are listed in the output.
Try to reinstall as the following (using an already installed bake instance, as in the manual):
mkdir dce
cd dce
~/bake/bake.py configure -e dce-linux-1.2
bake deploy
Then go in source/ns-3-dce and run the examples as in the documentation.
Note that after the installation of the dependencies, DCE does not need to run as root. Note also that you can always take one of the existing examples and use it as starting point.