下列哪句正確？

This is a typical "it-cleft" sentence using "introductory-it" to emphasize a part of the sentence.

Structure: It + [verb to be] + [noun/noun phrase (emphasis)] + [relative clause]


e.g. The film was made in Bristol. (original sentence)
===> It was Bristol in which the film was made. (cleft - emphasize "Bristol")

In this case, there are some other ways to write the relative clause as "Bristol" is a name of a place (city or town name).

(1) It was Bristol that the film was made in. (relative pronoun - "that")
(2) It was Bristol where the film was made. (relative adverb - "where")

Therefore, "It was in Bristol where the film was made" is wrong in grammar.

Moreover, if you want to emphasize the subject of the original sentence instead, the cleft sentence will look like this:

It was the film that was made in Bristol.

2012-07-15 01:12:35 補充：
因為作者可能除了想強調 Bristol 外，還想強調 in 來凸顯不是 at 或 on ，例 at her home 、on the island 等等。

"where" 已經代表 in, at , on , to,... a place

It was in Bristol where the film was made.- the 'where' may be a studio which is in Bristol.
It was Bristol where the film was made.- here 'where' means 'what city'

誰對誰錯？有其他人可以給點意見嗎？

Bristol是一個地方名，就算你不知是那裏，但句子的"where"提示你這是一個點，
所以
It was in Bristol where the film was made.
才是正確
地方名稱或地點一般要加preposition
in 或 at
要所指的範圍，in是比較宏觀或區域，at會更specific/確定位置(例如: at ABC Studio in Bristol或 at xxx Park/Mountain/Village in Bristol)
但這句的意思只是說出一個城市的地點吧，所以必要有in那地點的。

另外你可能會見過
It was David(Name) who made this film.
才不會有preposition在名稱前面。

Both are defining relative clauses eg:-It was in Bristol (Changed to that---)the film was made.
eg:-It was Bristol (Changed from where to that----)the film was made.
"where" ,adverb, used after phrase"was Bristol"that refer to a place or situation to mean"to which".

It was in Bristol where the film was made.
呢句係岩GE~

It was Bristol where the film was made. 呢句