Everybody can hear it when they have your finished skin.
extract the cultist model to your desktop (or wherever u want) and edit your own sound files with a program like COOL EDIT (there is a trial software for 30 days or like that) and then simply put them to your skin.(in an own direction called "SOUNDS").
Now open the sounds.cfg of the skin and remove whatever stands there.
Put your own sounds there then. (instead of cultist1m change it to the name of your skin for example SKIN1m)
Now you have models/players/cultist and other things like ext_data (when you created an own bot) and the directory sounds. Zip them up with winzip and chose the name, for example owncultist.pk3. Now put them in your gamedata/base directory and it should work. (and by the way you can reskin the cultist when you want as long as it isnt in the final pk3)
I hope all this wasnt for nothing and you are a beginner with skinning. If you arent, sry but that should be enough to tell you how it works with the sounds.