If you just want to kill any/all java processes, then all you need is;
killall java
If, however, you want to kill the wskInterface process in particular, then you're most of the way there, you just need to strip out the process id;
PID=`ps -ef | grep wskInterface | awk '{ print $2 }'`
kill -9 $PID
Should do it, there is probably an easier way though...