This appeared like a reasonable question at first.
Then it was reported as a possible duplicate. [Edit: Turns out it was an external reference, not on SE.]
Subsequently, it was revealed that it was posted by a bad user.
Now can we:
Merge the question with its original if any? [Edit: Not an option, external reference.]
Then convert the whole thing into Community Wiki question?
It depends on the policy, plus the merits of the question in question.
You cannot merge a question with something that is not even in the Stack Exchange site.
As for making a question Community Wiki, moderators can make any post Community Wiki, and make a Community Wiki post a normal one. The purpose of a CW question is not penalizing who answers a perfectly legitimate question, though; its purpose is avoiding somebody gets reputation for answering a question where all the answers are equally valid. At least that was the purpose of CW questions when CW questions were the way to legitimate subjective questions. Now questions need to be acceptable as they are, without being CW. (There is a blog article about the change of the CW question's purpose.)
It is true that, when a question is made CW, users who answered don't lose the reputation gained before the question is made CW, but it is also true they lose any reputation gained from future up-votes.
In this case, the OP gained 5 points, while each of the users who answered the question gained 40 points. The gain from the OP who is trying to workaround the suspension is very limited, compared to the users who answered what seems a perfectly acceptable question.
Rather than penalizing the users who answered, who cannot know if the account has been created from a suspended user, I would rather penalize the user who keeps asking questions when he is not allowed.
Let the questions not be CW; just prolong the suspension time for the suspended user, which means suspend him again when the current suspension ends.
I don't think it can be merged with a question asked somewhere else.
The question itself isn't a particularly bad question, in my opinion — it's not nearly as bad and unconstructive as most of his others. And it's got good answers which are better than those on the other site (as might be expected!)
I don't know whether making the question CW is possible for mods; it pulls the rug out from under the rep system. As I understand it, both answers would lose their rep.
As you say, each case needs to be considered individually, if only because the system forces each instance to be separately dealt with. In this case I would say that the question should stand; it's not a question worthy of closure on its own merits.
Now that the sockpuppet has been merged, the OP hasn't gained any rep from it yet, but his deliberate flouting of the rules means that his suspension must be permanent.
One of the functions of Community is to 'own community questions and answers so that nobody gets unnecessary reputation from them' (here is the first mention, but it was discussed here in relation to this very user), so surely good questions from a banned user should be transferred.
