i went to see him to find out what had happened
这里填的是to find不是see的宾语补语,不是him“弄清楚”,而是“我”弄清楚.我【为了弄清楚发生了什么事】,我去看望他.to find out what had happened不定式做目的状语有点明白，这个to find 是修饰i went to see him这个句子，可以这样理解吧？是的。to find out what had happened不定式短语做目的状语，是修饰i went to see him这个句子。