I'm pretty sure its in the user manual
lol... nope, anyway this is the general info:
"Symbols not on the keyboard. If you have a hardware keyboard that has a "Sym" button (often Fn + Space) you can use it to type symbols that aren't on the keyboard. For instance, say the keyboard has a "/" but no "\". Type "/" then hit Sym. It'll switch. Hit Sym again and it'll switch to "|". This is also a somewhat convenient way to get non-English characters. For instance, if you want an o with an umlaut over it, hit o and then hit the Sym key a few times. It'll cycle through the various accents. Or, if you need the Spanish ñ, hit n then Sym. "
So pretty much, the sym key(s) you can get are the ones that look like the key you pressed - you just have to play with it (say in notepad) to get an idea of what each does.