To kill a process you started using nohup you first need to get the "process number". To do so use the following Unix command
ps -ef | grep $USER | grep node
This will give you a listing of all of your running node.js jobs. For instance
gtowell 696622 1 0 Jan19 ? 00:00:02 node app5.js
gtowell 780122 1 0 Jan20 ? 00:00:01 node app6.js
gtowell 816188 816044 0 10:32 pts/0 00:00:00 grep --color=auto node
The process number is in the second column. So to kill the node process I started on Jan 19, I would enter
kill -9 696622