This post details where the SDA SCL pins used for I2C/TWI are available on Arduino’s.
I2C TWI pins on the Arduino
The SDA and SCL pins are the used for communication using the I2C/TWI protocols. These allow multiple devices to communicate the Arduino on a standard interface.
Most Arduino’s only have one set of these pins however the Due has two.
||I2C / TWI pins
||A4 (SDA), A5 (SCL)
||20 (SDA), 21 (SCL)
||2 (SDA), 3 (SCL)
||20 (SDA), 21 (SCL), SDA1, SCL1
For more information, you can read the Arduino page on the Wire library.