The code can be downloaded here.

You will find sound definitions in "Utils\Sound Control.h" enum "SoundDefines". You need Visual C++ to see the numbers of each enum.
For example "SOUNDS\Fridge Door Open.wav" in Sounds.xml is number 225 which equals "OPEN_DEFAULT_OPENABLE" in "Sound Control.h".

Function "PlayJA2Sample" in "Utils\Sound Control.cpp" gets called when a sound needs to be played. There are tons of places in the code that use this function. For example when a soldier uses a wirecutter the function gets called with the parameter "USE_WIRE_CUTTERS" which is 241. If you look at entry 241 in Sounds.xml you will find "SOUNDS\wirecutters.wav".

For opening containers you can take a look at function "GetStructureOpenSound" in "TileEngine\structure.cpp". From the looks of it the sound seems to depend on the material of the container.

You see that you can't simply add sounds for interactions without changing the code.