If you want know, the how may nodejs processes running then you can use this command
ps -aef | grep node
So it will give list of nodejs process with it's project name. It will be helpful when you are running multipe nodejs application & you want kill specific process for the specific project.
Above command will give output like
XXX 12886 1741 1 12:36 ? 00:00:05 /home/username/.nvm/versions/node/v9.2.0/bin/node --inspect-brk=43443 /node application running path.
So to kill you can use following command
kill -9 12886
So it will kill the spcefic node process