It would certify that he had specialized in pharmacy, but it would further certify that he had been exposed to some of the ideas （that）mankind has generated within its history.

划线部分是定语从句，修饰ideas。generate 是及物动词“产生”，关系代词作宾语，被省略。

【翻译】它（可能指《本草纲目》）将证明他专门从事过制药学，但它也将进一步证明，他已接触到人类在其历史中产生的一些思想。