Although What knowledge do the people of Westeros have about Daenerys and her dragons? is tagged game-of-thrones, the answers seem to be book-based, whereas the answer to Do Westerosi know and believe that Dany has grown-up and dangerous dragons? is primarily show-based. So one solution would be to retag the former as a-song-of-ice-and-fire and keep both questions intact.
That still leaves the problem of possible future incarnations of the same question. What will happen if someone posts the same question again asking who knows about Dany and her dragons in the books after The Winds of Winter has been published, or in the show after Season 7?
It's possible that she may actually show up in Westeros and declare herself in the next book/season, in which case the question will be moot since the answer will become obvious.
If not, the best suggestion I can come up with is to make the questions and their answers community-wiki and update them as new canon material is released. That way, anyone can edit the posts, and we'll have an up-to-date record of the latest and most accurate answer to the question in both the books and the show. Not only that, but we can record how the answer has changed over time, by listing the people who know in the order they find out.
We could also post a new CW question asking about both the books and the show, compose a really top-quality answer to it as described above, and close both the existing questions as dupes of that.
Alternatively, it's possible that you're just overthinking it and this won't become a problem :-)