It was twenty years ago before he returned to which he was b

It was twenty years ago before(改为that：强调句) he returned to which(改为where引导宾语从句） he was born and brought
就在20年前,他回到了生他养他的地方.(强调句的）
正常语序：
Twenty years ago,he returned to where he was born and brought up.
也可以说：
Twenty years ago,he returned to the place where he was born and brought up.
returned to the place where(用where不用which) he was born and brought up,

Bingo!，you got the answer!

题目上的句子中的which应该换成where, where he was born and brough 可以看成作介词to的宾语从句。题目中的before是没有错的，按照您的说法，‘returned to the place which he was born’
which前面应该再加个in或者干脆把which换成where也讲得通。