The MAX17055 supports the slave address 0x6C (or 0x36 for 7 MSbit address).
Regardless of the fuel gauge configuration, if the I2C bus is functional, you will be able to read Vcell content. If you have the battery cell is connected, then you will be able to read Vcell content since device will make the analog reading and register will be populated with raw data.
In term of troubleshooting I2C communication, we recommend to monitor the SDA and SCL on the scope to ensure they are transferring data as expected and ensure the none of these lines are held low for any reason, that will prevent host from reading values from the device.