The Adafruit Shield v.5 ? https://www.adafruit.com/product/51
That shield does not have the SDA and SCL near the USB connector yet.
You can use A4 (SDA) and A5 (SCL).
[ADDED] There is also a "Sensor shield V5", that does also not have the SDA and SCL pins near the USB connector. You can use A4 and A5, but there are also 4 pins in the middle of the board for the I2C bus.