Sorry if i posted in the wrong spot .... Well im new to freenas i dont know how to find the folder to put the plugin in ....
But see that's where it's a broad question. There are multiple ways of installing and running a Plex server.
I'm going to assume you used the "plugin method", rather than the better updated manual installation method.
Look in /var/db/Plex? Inside the jail.
If you're connecting to your server via sftp, look at /mnt/poolname/jailsdatasetname/plexmediaserver_1/var/db/Plex?