I2C devices are identified to their master (that is, our Raspberry Pi) by a unique address, and the default address for the ADS1115 is 0x48. Since I2C devices are addressed, multiple devices can share the same I2C channels (pins) on a Raspberry Pi.
You can change the I2C devices on most IC2 devices if you have multiple devices sharing the same address. This is the purpose of the ADDR terminal on the ADS1115, and you can find instructions for its use in the ADS1115 datasheet.
Raspbian OS contains the i2cdetect utility that queries the Raspberry Pi's I2C interface for connected devices. Run the following in a Terminal:
$ i2cdetect -y 1
The -y option assumes we answer yes to any prompts. 1 is the I2C bus number. It's always 1 on the Raspberry Pi 3 or 4. We expect to see the output like this:
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- --...
