So I have to Skype with someone, but he is not...well let's just say not a "geek", so I have to log in via SSH to his Fedora machine, and turn on sound [because he can't hear me when using Skype, but I can hear him, so the sound is turned off/too quiet on his side]. How?
You can usually use
alsamixer from a command line over SSH to control ALSA sound levels. For a less graphical alternative you can use
If the system uses OSS instead of ALSA,
aumix should do the job.
As a last resort you could use X forwarding to send any other graphical sound control program back to your desktop for control.