I am speaking both for myself and others as well. I would greatly appreciate and utilize a site that one could ask where to ask a certain question. I have seen questions like that on this site, but instead of asking a question here, which is for the improvement of the site, why not create a dedicated site just for where to ask questions?
Personally, I don't really think this works with the Stack Exchange model. The topic of this site would be
"Is this question on-topic for Stack Exchange sites? If so, which one does it fit best in?"
It seems to me that the only experts on that topic would be regular users of the various sites, or possibly people that have read (in detail) the various per-site metas and FAQs.
These questions would probably be a good fit for the per-site metas, actually. From your comment:
"...I have a question that applies to both electrical engineering and software development, so where should I ask it?"
It seems that you could post your proposed question to the Electical Engineering meta, and say "Is this question a good fit for the site?". Those would be the most qualified people to answer that.
If you cannot narrow your domain down to one or two potential SE sites (and thus ask on their meta), then perhaps you need to put some more thought into your question =)