I likely haven't even downloaded the version that you are using, so I can only give information in general concepts. Also, I should mention that I'm about to go to sleep, so this will be my last quick response.

Basically, in expert mode you bypass the Knoppix automatic detection and tell it what hardware you have. This may allow you to bypass faulty detection that causing a hang. Just boot knoppix and type expert at the boot prompt. I suggest taking good notes on how you answer the questions; and if you do hang try again and answer the question that led to the hang differently. Also, you might want to do a Google search on knoppix expert mode (always good advice before asking this type of question). There might be a "cheat code" that would help you get past the hang, but I have never heard of a hang at this point, so I don't know what to suggest. However someone else might be able to make more suggestions or I may come up with something myself if you learn anything from your experiments with expert mode.

And I'm assuming that you confirmed with as md5 test that you have a good ISO download before burning the Knoppix disc, and that you burnt at low speed, otherwise you might just be hanging because you have a bad disc and expert mode isn't going to help that.