The what with the who? That's wayyyy too technical for a layperson like me. I forget what it's called...it's a simple cord with what looks like a standard 1/8" headphone jack on each end. Plug it into the Nomad, plug it into the MP3 jack, and I'm good to go. Sorry I don't have much more info...
By the way, I can't say enough good things about the Nomad Jukebox 3. It's worked beautifully so far, holds more than the iPod, has way more features (recording, line-in, 2 line-outs, all sorts of audio controls) and has easily-replaced batteries (which I guess the iPod doesn't). Oh, and bonus - it's silver and blue, so it matches my Element's interior perfectly.