For example, asking about the identity of real people appearing on the game. Another example is about the existence of a place or any object inside the game in real life. Is that OK?
Check this question: Who are really the people in the photo found in the Soviet installation
Is it OK to ask about the origin of contents of the game in real life?
Yes, as long as the question is also within the scope of acceptable questions for the site.
For example, asking about the identity of real people appearing on the game.
There are plenty of questions here regarding the identity of real people in the game. For example, this query shows a number of questions for people who provided voice acting in a game:
https://gaming.stackexchange.com/search?q=who+voiced
You can assume that someone on the site has the capabilities of researching this type of information for you.
Another example is about the existence of a place or any object inside the game in real life. Is that OK?
Yes. Here is one such example:
What parts of Fallout: New Vegas are based on the real world?
Check this question: Who are really the people in the photo found in the Soviet installation
I didn't vote to close the question, so I can't speak for the people who did. However, I can see a problem with the question.
My question is, it's a real photo of real people. Who are they? and how the game creators got their permission to use the photo?
The first part is essentially asking who are the people in the photograph. I believe that part is fine. I can't see why that would be off-topic.
The second part of the question asks about getting permission. That seems to be off-topic. This is regarding game design and not gaming itself.
So essentially, you can ask "Who are the people in the picture?" but not "How did the developers obtain permission for using the picture in the game?".
It may be worth attaching a screenshot of the picture to the question if you choose to amend it (i.e. attempt to make it on-topic).
If I am mistaken could you let me know.
