"Who should rule over us?"
Translation:Kiu devus regi super ni?
I don't think you can use "regi" like that.
"Regi" can be used transitively, but the object appears to be either a group or organisation (rule a country) or something that you control individually (regi ĉevalon). Neither is what a king does to individual people - you're not puppets whose sticks get pulled by him.
That more abstract "rule" seems to be "regi super (iu)".
???? When did it start that "should" has to be translated with "devas" instead of "devus"? "Who should rule over us" and "Kiu devas regi nin?" is the correct translation? This would mean - the other way round - "devas" means "should" and not "must"???? I cannot believe that.
Should and would are confusing words in English. Their meaning has changed in the last century. Compare them with shall and will.
I usually use "should" in the old fashioned sense when I am being formal in a request for something: "I should be grateful if you would ...". It doesn't mean "ought to" in this sense it means that the feeling of gratitude is going to (must) occur when the request is fulfilled.
--you cannot use an imperative in a question...-- [P.S.: I was wrong reg. Esp., see below]
(and "kiu regus nin?" would be semantically different - more like 'who would rule over us?' [after the last king dies... / when the election does not lead to the forming of a stable government])
I think you can use an imperative in a question.
PMEG agrees: http://bertilow.com/pmeg/gramatiko/verboj/vola.html has the example Ĉu ni iru al la dancejo?
Kiu faru tion? sounds fine to me as well - "Who should do that?" or something like that.
The imperative here "montras, ke la ago aŭ stato ne estas reala, sed dezirata, volata, ordonata aŭ celata" -- in this case, the "doing that" is desired but the doer of this desired with is in question.
devus, volus and povus can act a bit differently from other conditional verbs. This gives a good explanation. https://adventuresinesperanto.wordpress.com/2011/07/29/should-a-would-a-could-a/ We do something similar in English: 'I would like' can be a polite way of saying 'I want' as well as a condition statement. (I think (though not sure) that 'Je voudrais' is similar in French, is a conditional form of the verb 'to want' but also a polite way of asking for something).