Cognitively means “in a way that has to do with cognition”: with the mind’s knowing, understanding, or learning. It tells you which side of a person or a task you are talking about. A job can be easy for the body but cognitively hard (your body is fine; your mind is busy). It is a formal adverb, common in research and education writing, not in street talk. You can often say the same thing with “for the mind” or “in terms of knowing and learning” if the long adverb feels heavy. It does not mean “cleverly,” and it does not mean “on purpose.”