Who would have thought that instead of getting square-eyed from watching too much TV, Malcolm was getting sore-eyed from spending too much time scribbling in his leather-bound diary late at night?

who 是疑问代词，表示"谁"，用于提问或引导疑问句。 would 是情态动词，在这里表示假设或推测的语气，意思是"会"。 have 是助动词，与过去分词 thought 构成完成时态，表示"已经"。 thought 是动词 think 的过去分词，意思是"想、认为"。 who would have thought 是一个固定表达，字面意思是"谁会想到"，用于表示对某件出乎意料的事情的惊讶或感叹。