If there is a reason to close it, then you should vote to close the question (or flag the question to be closed); the fact the question doesn't show code is not a reason to close it, but if the question is not answerable in its current form, then you can vote to close it as "not a real question," if it is not possible to understand what being asked; as "not constructive," if the question is asking an opinion, or would generate debates; as "too localized," if the question would not help any future users.
Apart the case of the question being spam, offensive, or containing hate speech, I don't see other reason to flag a question. I would not flag it as "very low quality," as that would just move the task to somebody else (the moderators) who could not do something more than a user could do; they could eventually close the question, but so far I have not seen a question being closed for being low quality. If the question's quality is low, and you can edit it, you should edit it; if the question's quality is very low, and it is not possible to understand what being asked, you could down-vote it. In any case, you should not flag a question for moderation attention, when there is something you can do.
Moderators are human exception handlers, and you should not invoke their action just because you don't like the question.