I was wondering, if I have a question that isn't, or just barely related, to any of the SE sites. Where do I ask this? Is there any place on SE that covers these questions?
As it stands, if your question is not on topic for any of the current stack exchange websites, then you need to go elsewhere. There are plenty of forums for the many different topics not covered by Stack Exchange sites.
If you feel the topic is something that should have its own stack exchange site, you can propose one on Area 51.
If you ask a question on a site wherein it would be considered 'off-topic,' then it will be closed as such; which makes the exercise rather pointless for you, and irritating to those that have to close (yet another) off-topic question.
If you feel that there is an area that would be appropriate to your question that isn't currently served by Stack Exchange, it would be best to make a proposal for such a site/interest at Area 51.