Final answer:
The adverb 'already' describes the verb 'looked' in the sentence.
Step-by-step explanation:
The adverb 'already' describes the verb 'looked' in the sentence. It tells us when Joe West looked for his missing backpack, which is that he looked for it at a time prior to the current moment. In this case, it indicates that Joe West had already looked for his backpack before the current moment.
Learn more about Adverbs and verb descriptions