Final answer:
The infant learns to climb up on the sofa by watching his older sibling through observational learning.
Step-by-step explanation:
The type of learning that an infant uses to climb up on the living room sofa by watching his older sibling is observational learning. Observational learning is a process in which individuals learn by observing others and then imitating their behavior. By watching his older sibling, the infant can learn the specific actions and movements required to climb up on the sofa.