這是一個complex sentence
main clause: He tried to find out the way(受詞是不定詞片語to find out the way)
dependent clause: in which his best friend learned English well(它的先行詞為way,本附屬子句當作way的修飾語,為形容詞性質,屬限定性質)
He-----S
tried-----V
to find out-------inf.phr.,co-ord. to tried
in which-----which=rel.cl. when specifing the friend,John talking about, giving INFO about him;
learned---(has learned)----past participle
English well------going back to learned=learned well (adv);-----in which Eng.=O