Knemo is working here on Slackware 14.1, albeit first I had to configure It that way: from the system tray,
right click->Configure KNemo...->Misc in Backend, I switched from "Nettools" to "Sys"
Once the "Sys" backend was selected, I could see the data flow in the window "Open Traffic Plotter" I didn't push further the test...
That being said, Slackware still uses the ancient convention to name network cards (eth0, Wlan0, etc); my card is named Wlan0 for instance.
Can someone from the Deb world give this a try and report back if, at least, the right name for the card is used?