the syntax is "IP:<Your_NFS_Export>/clonezilla..." correct? But what comes after the ip adress?
We can't answer this for you. You have to have a nfs share created and we don't know what that is called. But if you enable nfs and create an nfs share from the same shared folder that you use in the pxe plugin settings tab (lets call it pxefolder) and your server's ip address is 192.168.174.43 then that part of the line would be: 192.168.174.43:/export/pxefolder
I suggest reading a bit more about pxe booting and nfs shares. The plugin can't do everything to setup the images.