There are several problems with the device and code combination you linked in post #1.
First, the device link is for a 5v 16bit DAC, not an ADC as you say you want to interface. Moreover since the DAC is a 5v device, I doubt that it will be compatible with the 3.3v Teensy 3.6 which is not 5v tolerant.
Second, the code you linked is for a 12bit ADC whoes I2C address is hardcoded as 0x29 (the I2C address for the linked DAC is 0xC). In addition, the code is written for the Particle development environment and makes function calls that, to my knowledge, are not supported in the Arduino environment which is what Teensy code development is based on.
I think you should do a bit more research and carefully read the product literature before spending $80 for a 4 channel DAC if what you really want is an I2C ADC module. Also if you are not comfortable writing the interface code yourself, you should look for one that is supported by code written for the Arduino environment.