if you want to kill a specific node process , you can go to command line route and type:
ps aux | grep node
to get a list of all node process ids. now you can get your process id(pid), then do:
kill -9 PID
and if you want to kill all node processes then do:
killall -9 node
-9 switch is like end task on windows. it will force the process to end. you can do:
kill -l
to see all switches of kill command and their comments.