liljone :
If I Copy knoppix to a flash drive.
If you "Copy knoppix" to a hard drive - you wouldn't be able to boot from that hard drive.
You'd need to install the OS to your drive - HDD or Flash.
Also the PC has to support booting from a USB flash drive. Not all PC's BIOS allow for that.
The flash drive must have boot sector area created with special utilities and the flash drive must contain the boot/system files.