Stackoverflow link: https://stackoverflow.com/questions/14930329/finding-ip-of-a-jenkins-node
blog on setting up a node: https://embeddedartistry.com/blog/2017/12/22/jenkins-configuring-a-linux-slave-node
There are great answers in the stackoverflow post on using the script console but in the event you found yourself with just the Jenkins directory or no access to the script console it's pretty easy to get this information.
You can just browse to jenkins-ip/computer/$nodename/config.xml. This request will require the extended read permission.
Optionally if you are on the box or have a backup you can go to jenkins-dir/nodes/$nodename/config.xml