# To list any process listening to the port 8080:
lsof -i:8080
# To kill any process listening to the port 8080:
kill $(lsof -t -i:8080)
# or more violently:
kill -9 $(lsof -t -i:8080)
# (-9 corresponds to the SIGKILL - terminate immediately/hard kill signal: see List of Kill Signals and What is the purpose of the -9 option in the kill command?. If no signal is specified to kill, the TERM signal a.k.a. -15 or soft kill is sent, which sometimes isn't enough to kill a process.).
You want to use backtick not regular tick:
sudo kill -9 `sudo lsof -t -i:9001`
If that doesn't work you could also use $() for command interpolation:
sudo kill -9 $(sudo lsof -t -i:9001)
#list process running on specified port (here 80, change to your port)
sudo lsof -i:80
#kill process on specified port (here 80, change to your port)
sudo kill $(sudo lsof -t -i:80)