Final answer:
A nurse should assign Defensive coping as the nursing diagnosis to a client needing assistance with assertiveness.
Step-by-step explanation:
A nurse should assign Defensive coping as the nursing diagnosis to a client needing assistance with assertiveness. Defensive coping refers to the use of defense mechanisms to protect oneself from anxiety or emotional distress. In this case, the client may be experiencing difficulty in asserting themselves and may use defense mechanisms, such as avoidance or aggression, as a way to cope with their assertiveness challenges.