Which HR function involves offering programs through which employees acquire knowledge, skills, and behavior that improve their ability to meet the challenges of a variety of new or existing jobs, including the client and customer demands of those jobs?

The answer is: Training and Development

Explanation:

Training and development are designed to enhance the employee's current or future performance on his existing job or even a new job. This is done by improving his abilities through education, new skills, leadership training, knowledge in a particular subject and professional development.