"Knowledge" is the level of education that an individual must have at a minimum to be considered qualified for a role.
"Ability" is an inborn quality that one ‘does’ or does not possess. Ability is not something that can be learned or developed unless it is there, to begin with.
"Skills" - Specific learned abilities that you will require to perform a given job successfully.
"Competencies" - Knowledge & behaviours that lead you to be successful in a job.
10 Qualities I admire more than Skills
Courtesy: Sarvesh Kumar Gupta