Now I would like to insert a BMP280 I2C sensor in the system so somehow I have to address the RTC module when I'm manipulating it and than the sensor.
I wasn't able to find any instruction how to address the RTC module in this case. Please advise. Thanks.
The Christensen DS3232RTC library does that for you. The address of the RTC is at 0x68, and the library includes this code and all the addressing takes place behind the scene
// DS3232 I2C Address
#define RTC_ADDR 0x68