We have a section in the wiki about wireless networking, although contributions to it have be, to put it kindly, "light". In my own experience the one wireless NIC that I have that worked under 4.02 (a Belkin 802.11b pcmcia card) no longer seems to work with 5.0.1 (it's apparently recognized but I can't convince the software to set it up and use it.

I also have two D-link DWL-650 Rev M 802.1b pcmcia cards, but Knoppix has never worked with them. Same for a Belkin 802.11g card. The strange thing is that I'm finding some other Linux distros work with these cards. Ubunto recognized the DWL-650s and even picked my SSID out of thin air (literally), all I had to do was set up my encryption key and I was good to go. And interestingly enough Ubuntu identified the chipset as a Realtek RK8180L, and this seems to be a highly recommended chipset for Linux wifi nics, but D-link shows no Linux driver for it and Knoppix ignores it. And unfortunately there isn't much software available on the Ubuntu Live CD (and strangely the Ubuntu Live DVD seems to have exactly the same software installed as the Live CD, nothing more!)

I have also come across a Live CD recently that reciognizes the above 802.11g card that Knoppix doesn't, although I forget which. Might have been Mandirva or Puppy Linux.

So sadly I can't recommend a card, both because manufacturers have discontinued many of the 802.11b cards that used to work, and because the too often release cards with different chipsets under the same model number, and because the current Knoppix is failing even on some cards that did work in the past.