句子主干是：It seems impossible for us to read anything
只不过后面的独立主格部分比较繁琐：without the mind making reference to the framework knowledge_____has already acquired.
至于空格出该怎么填,第一要明确这个末尾部分的谓语has already acquired是谁发出的.这里对象只有mind思维和knowledge知识,显然是“大脑思维”获得,而非“知识”获得；所以这里的主客体关系是“大脑思维获得知识”,再理解下填入it后句子如何分析：
without the mind making reference to the framework knowledge （it has already acquired）,
it指代mind,并且括号内是以the framework knowledge 为先行词的定语从句,所以这里其实是把that/which省略了（因为在从句中作的是宾语）
原句是：
It seems impossible for us to read anything without the mind making reference to the framework knowledge （which/that）it has already acquired.
翻译：如果思维不能很好的与我们大脑所获得的知识框架联系起来,似乎我们什么也读不懂.