If you're asking 'who did something?', do you always need to use this reported past tense? After all, you weren't there, or you would know the answer. Or can you still use the other past tense if you can see with your own eyes that it was done, even though you don't know who did it? (Blimey, this reported past tense is taking us into deep waters.)
There've been other sentences using the regular past tense in questions like this ... I think the difference might be that in this case the speaker doesn't expect the person they're asking to know directly? Like, they're expecting that the person's response would use -mış? But if the speaker thought the other person had actually witnessed the event themself, then you'd use the regular past tense. That's the impression I get anyways, I could be way off for all I know
Not really...I have a gut feeling that "preserve" is mostly used when talking about protecting abstract concepts like beauty, nature, or silence. A long time ago (like Shakespeare's time), "preserve" and "protect" were interchangeable.
If you talk about preserving a book, it sounds like you are making jam with the book or drying it out like beef jerky. :)
This would usually be one of the most accurate translations of a -miş sentence but not always. You can also use -miş if you hear something done or happened from the person who actually did that. So in this case it wouldn't make sense to use this translation. Example:
Ali: "Okuldayım." - Ali: "I am at school."
You: "Ali okula gitmiş." - "Ali went to school." (You heard this from Ali himself, not from somebody else)
The problem is in the English. "Is protected" would be a passive voice verb, so you would be asking about the "who" that was protected, rather than the book that was protected. Your sentence doesn't quite make sense, but "Who is protected BY that book?" would be asking about which person was cowering behind the giant book or maybe was guarded by the magical spells in the book. Here, it is the "who" that was the guard, protecting the book. It is also in the past tense, which can be a bit confusing in English, I suppose, since "protected" is a verb in the simple past tense or a past participle, but if we put that past participle with the present tense of the verb "to be," it becomes a present passive verb.