If the file is within the "Sounds" folder, the "{VA_SOUNDS}" token can be used to set that path dynamically, so that it points to the correct location regardless of where VoiceAttack is installed.
Normally if you use the file picker of the "Play a Sound" or "Play a Random Sound" actions, that token will automatically be inserted (provided the chosen file or directory is within the "Sounds" folder, obviously).
If you're distributing sounds (that you own or license the copyright to) with a profile, you may want to look into .vax packaging, so you can have VoiceAttack copy the sounds to the proper folder when the profile is imported.
Press F1 while VoiceAttack has focus to open VoiceAttackHelp.pdf in your default PDF viewer, and navigate to the "VoiceAttack Profile Package Reference" section for more information on that.