Where do I look for Linux kernel module documentation?
For example, I've tried googling the module
iwlagn, but I cannot find anything that tells me about available options. Where do I look?
You have two authoritative sources for module information:
And of course, google is your friend here too, once you found the options of interest to you, googling them together with the module name sometimes gives useful results.
You normally should not directly configure your modules with options, rather you should use the software your OS provides for configuration. In case of wireless LAN you'd better use
I just binged for your module and found this description that I found rather complete. You should have seen it too. Did you miss anything there?