Unique GPUs/Graphics cards need Linux drivers. Could be downloaded from the website of the Nvidia website, Debian section.
Have you read all sections of cheat codes and tried them, using the init 3 instead of the graphical mode? Please log on to your regular OS and read the help files available with your knoppix distribution iso/DVD/pendrive.

Your would have been better served by posting your system details, if you have a Debian system installed, using the hardinfo package.

Kindly be informed that Knoppix would boot easily without trouble on some of the general lap/desk-tops available on the market. But there are a bewildering variety of combinations of components available. So one should begin by using cheatcodes and then proceed step by step.