So I created a trigger_multiple. Made it trigger_once and clientside_trigger.
After that I created script_struct with KVP script_sound.
After that I selected my trigger and then selected script_struct and pressed "w".
But the sound is not working in the game when I am passing trigger_multiple area.
Am I doing something wrong?

Yes, you shouldn't use a script_struct and yes use a sound looper.
 

I got the sound working, but it does not depends on trigger, it is just playing.
And simply connecting them with "W" key is doing nothing. Can anyone provide an example of simple sound, that activates by multiple_trigger (only once).