The mobility plugin for cooja can be found at this URL

http://sourceforge.net/p/contiki-NGprojects/code/HEAD/tree/sics.se/mobility/

Create a new directory at --> cd contiki-NG/tools/cooja/apps

mkdir mobility

Download and Save all the files into this mobility folder

Navigate to

cd contiki-NG/tools/cooja/apps/mobility

sudo ant jar

This will build the plugin

Start Cooja Simulator

cd contiki-NG/tools/cooja

sudo ant run

In Cooja,
Settings > External Tools Path…

Edit Settings Screen will pop-up

Scroll down to DEFAULT_PROJECTDIRS
This field is used to specify paths to all the plugins in Cooja Simulator
Here you have to add a path to the downloaded plugin.
Go the end of this field DEFAULT_PROJECTDIRS
Insert ‘ ; ‘ symbol
Add the plugin’s path
[contiki-NG_DIR]/tools/cooja/apps/mobility
Click Save
Close Cooja Simulator and Start it again.
cd contiki-NG/tools/cooja/
sudo ant run
Now go to
Settings>Cooja Extensions
Cooja Extensions Window will pop-up.
Scroll down to mobility select it and click on “Apply for the session”

Under the Tools tab in Cooja you should see a new “Mobility…” option now