Wh-questions in Chinese
Tl;dr: Placement depends on whether the wh-word is the subject or object of the sentence, and whether emphasis is intended.

Given both Chinese and English follow the SVO structure (hence their comparability), fronting in English (or the in-situ-ness of Chinese) is best observed when the wh-word is the object of the sentence:





Wh-word
Chinese
English




Subject
a. 誰偷了蘋果？
Who stole the apple?


Object
b. 瑪莉看見了誰？
Who did Mary see?





In Chinese, it is unideal when there are two doer-action pairs in a single sentence. For simplicity, let us consider Which picture he took did she post? instead (the she–post part is still grammatically identical to the original sentence - no loss of generality). Now following the logic in 1., since which picture he took is the object, shouldn't that be placed at the end of the sentence? Yes and no, depending on whether emphasis is intended. Therefore,





Emphasis
Chinese
English




–
a. 她發佈了哪張他拍的照片呢？
Which picture he took did she post?


+
b. 哪張他拍的照片是她發佈了的呢？
Which picture he took is the one she posted?





In fact in sentence 2b. (both Chinese and English), the picture has become the subject. Also, notice how the 是～的 has been insidiously added in sentence 2b. That is precisely for emphasis. Without it, the sentence would sound awkward. (In fact, to aid your understanding, you may consider 哪張他拍的照片是她發佈了的*照片*呢？: the analogous structure of this hidden 照片 is the one in English, which is normally omitted in Chinese.) Have a look at example 5 of this link.

Of course you may argue sentence 1b. can also be phrased as 誰被瑪莉看見了？, apparently violating the in-situ rule. But technically this sentence is in the passive voice, which also changes the object of its active voice analogue (誰) into the subject.