An overview of the onboard I2C devices is available here.
List all available I2C busses:
i2c bus
Select the I2C bus device
i2c dev 0
Show all devices connected to the currently selected I2C bus:
i2c probe
List all available I2C busses:
i2cdetect -l
Detect all devices connected to an I2C bus:
i2cdetect 0