Knob cheese is a slang term or euphemism for smegma, the dead skin and other build-up that occurs between the foreskin and penis of an uncircumcised male. Removing or otherwise getting rid of the smegma is simply a matter of daily hygiene practices. If cleaning does not take care of the build-up, there may be an infection or something more serious occurring, for which you should consult your doctor.
Purchase an antibacterial soap, such as Dial or Safeguard. This will help with any associated odours in the groin or genital region.
Draw a hot bath or shower. Hot water and antibacterial soap provide your best defence against odours and infection. Wet the washcloth and lather the soap, then draw the foreskin back from the gland.
Wash the area beneath the retracted foreskin. You may need to scrub with the washcloth several times. When finished, shower or bathe as normal.
Remember that smegma does serve a purpose, and some smegma is both healthy and necessary. Don't over-clean the area, which can lead to painful intercourse.