It sounds like you are making something for NWN:EE and not NWN2, or am I mistaken?
If you are working with NWN2 nonetheless, check out this thread. Even if you’re in NWN:EE this might help:
EDIT: If you don’t want to read you could try something like this:
object oPC = GetPCSpeaker();
object oPlaceable = GetNearestObjectToLocation(OBJECT_TYPE_PLACEABLE, GetLocation(oPC));
AssignCommand(oPlaceable, PlaySound("gong_hit", TRUE));
You need a placeable nearby then (which you have with the gong already) so I think it should work.