You are going to need two things:
First, some documentation on the code running in the Fanuc PLC. Specifically, you need to know where the desired data resides in the controller's memory map.
Second, you'll need some sort of way to communicate with the PLC. If the PLC can communicate via a standard protocol like Modbus you have it made! Do a search in the responses on this forum for "Modbus" and you'll find literally dozens of sources for LV Modbus drivers.
Failing the ability to establish connection via some sort of atandard protocol, you might have to get a little "creative". I once had a contract where I had to get data from an old TI PLC that had a fried serial port on it so I could talk to it using TI's native NITP protocol. The controller did ho
wever have a BASIC programming module on it that had it's own (functional) serial port.
Making use of that BASIC programability I wrote a command interpretter that had only one mnemonic command: GMTD (give me the data). When it received this command it would spit-out the 5 or 6 values I needed over it's serial port.
Hope this helps,
Mike...