if you have a DFM (OnCommand Unified Manager) server, you can set up an alarm there to (eg) email you when either the inode almost full or inode full thresholds is passed.
you could run a PowerShell script to report on the inode usage. For example, something like this would generate a list of volumes sorted in descending order of % inode usage (ie the ones shown first are the ones with the highest usage)
The DFM server software is a free download but you will need a licence key to install it. The key is free -- just contact your NetApp account manager.
Once you have it in place, you create an account on the NetApp side which is used to poll the filer. To make alerts happen more quickly, you can also send SNMP traps from the filer(s) to the DFM server.
If you have clustered ONTAP, there is a newer version (6.x series) for that with a greatly improved user interface BUT no reporting capability so start with the 5.X series of releases.