Can i make this old pentax lens work on my pentax DSLR K20D?

Id it has a Pentax K bayonet fitting, then it will work, but you may not be able to use auto focus. If it is a Pentax screw fitting, then you van get an adaptor, but no automatic functions will work. If if is, by any chance, a Pentax KR fitting do not, under any cirstances, fit it to your camera, it will lock on but you will beundable to remove it.