I just saw on http://knopper.net/knoppix/knoppix704-en.html that
"Optional 64-bit Kernel via boot option "knoppix64", supporting systems with more than 4GB of RAM and chroot to 64-bit installations for system rescue tasks (DVD version only). "

so I have to download and install the DVD version?

Then I can run flash-knoppix to create a bootable USB stick?

Am I correct? I will let you know