For example, should my following question be on-topic? I have desperately looked for places to ask such questions, and was the main reason for joining the Engineering SE site (among others with fingers crossed)
Conforming to legislation is an important part of engineering.
I would expect to be able to ask and answer questions about engineering legislation on this site; from how to comply, to what our duties are.
The fact that an engineer has been able to answer your question, further confirms this; in my view.
In this case they're specifying EMI/EMC, in which case it could go here or possibly do better on EE.SE.
That said, as the answer to that question points out with LVD, EMI/EMC isn't all there is to getting a CE mark. Depending on the type of device, the safety requirements (61010-1 etc) can be a bigger hurdle than EMI/EMC and encompass more than just EE issues alone.