Recently, this question about Eladrin's Fey Step brought some confusion because Eladrin is "talked about" in DMG as an Example Subrace (for creating new subraces) while the actual, playable/official subrace was published in MToF.
In D&D questions (in particular for 5e, which I'm obviously more active), it's also common that the asker uses some random Homebrew content from the wiki, or simply states "the feature X of monster Y" - without quoting the feature X or telling us where the monster Y can be found. While it might seem laziness from me, I would prefer the asker to tell us where he found that. Also, it seems obvious that the Ancient Red Dragon he's talking about is the one on MM, but people might not remember instantly where the heck Boneclaw was published, and at first google glance the top result is a bad link for a homebrew in dandwiki.
Point being: Asker stating his sources makes the question more clear, easier to answer and requires less effort from the asker than from the answerer to remember/guess the source. We have high standards for source-citing for answers, but questions seem to be at some lower steps.
So... Can we encourage the asker to put that in the question? Can we, ourselves, edit the questions and add that info whenever possible? And do we have other options to encourage that behaviour?