It is not required to have an explicit cite for a claim in questions, though it is very helpful if the notability of the claim is questioned.
If you suspect that a claim is not notable, you should perform a minimum amount of research before acting. Performing a quick google search using search terms taken from the question is a good idea.
Is it true that an explicit citation is not required in questions? Even if it wasn't required in the past, should it be required in the future?
People have difficulty answering the question when there's no citation.
A typical example is Can the UK fire its nuclear weapons without US agreement?
The problems, the reasons why I think that all claims should include a reference by default, are:
When a user posts an unreferenced claim, then the claim as it's phrased is often very brief, vague or imprecise ... which means that people need to use comments to question what the question really means and exactly what it's asking.
If you do a quick Google search then you may find many slightly different variations on the claim, and it's not possible to know which one to answer
The person who is asking the question should be able to do the Google search themselves, if the claim is notable. Their doing that minimum of research improves the question; but if/when someone else does the research and edits the question, that is a perhaps unwarranted change to the meaning or intent of the question.
In contrast, a referenced claim is better:
- The original reference is longer (with more text), so that people can read it to understand the context, the exact words being used (not a semi-accurate paraphrase which is merely the understanding/memory/summary of the person asking the question here) and therefore the implied or exact meaning of the claim.
- If or when the meaning of the original reference is unclear, nevertheless the reference itself is then ipso facto on topic (the fact that it's referenced makes it notable almost by definition, except when it's from a joke or fictional source which nobody was meant to believe). The lack of clarity or ambiguity then becomes on topic, and deserves being answered in an answer instead of being questioned in a comment.
Alternatively, is it appropriate to simply flag a moderator if you think that an unreferenced question should have a reference: instead of posting a comment to the user, which the user may not reply to? Moderators have the ability to post a standard/canned/boilerplate comment, and/or to put a question on Hold, which may be better than (or supplement) a user comment.
I don't understand why the "rule" is ambiguous: why or when is it "should" (usually) provide a reference in questions, instead of "must" (always) provide a reference?
See also FAQ: Must all questions be notable?