It is certainly important to differentiate between knowledge, skills, and abilities (KSA’s) in your own mind when writing a job description. However, it is not necessary to list them all under specific headings when you write the description.
It is important to keep the differences between these three things in mind as you compose the description. This is so that you will not forget to include any of the three in the description. You will need to ask yourself if you have remembered to include each of the KSA’s in your description. But you do not necessarily have to label each of these in the job description. Applicants do not need to be told which things are knowledge, which are skills, and which are abilities.