You need a datasheet for the chip. Read that. Then read up on the Wire library, you'll need it to send the I2C commands.
As I stated, I cannot find any info on this chip or the new ones (they are black epoxy covered).
If you went to the link, you would have seen where they guy on the blog is in the same boat. He has a toner chip that he knows nothing about. He wrote some Arduino code to scan the I2C bus until it finds a device:
"I never used the wire library before and I was surprised by the small number of methods it has.
On Wikipedia I read each device on a I2C-Bus has it's own 7-bit address and to communicate with it you have to know this address. So firstly I wrote a function to scan for devices on the bus. My idea was to try to read from each possible address and to listen for answers. This worked excelently I found the chip at the first try."
Is this not possible to just scan the I2C bus until you find the device? It seemed to work for this guy. However I can't seem to get it to work with mine and could use some help from people much smarter than me. 
Doing a google search you can find pre programmed modules that you replace the old one with. I'm not sure if you have modules like this because the chips cannot be re-programmed and the toner level is estimated by the printer firmware. Something like the amount of pages the printer has done.
Yes, I have done this to purchase new toner chips. You are also correct in that the toner chip comes pre-programmed with a number that the printer deducts from (and writes back to the chip) until it is at zero. Then, no matter how much toner you actually have left, you have to get a new toner (or at least a new toner chip).
All of that is documented very well on the link I posted above.
I'm not averse to just purchasing new toners, but I thought this would be a fun project to dump the eeprom content from each new toner chip (C, M, Y, K), then have an Arduino uno with four colored buttons that will write that content (based on the button color and matching toner color) to a spent toner chip to 'reset' it..