Translation:On air the investigator asked who can speak Korean.
Quote marks are for direct quotation.
With indirect quotation (reported speech) like in this sentence when translated to English, 'backshift' must be applied. So the tense of the reported clause needs to move back one tense.
(1) Direct quotation (라고) :
조사관은 "누가 한국어를 말할 수 있어요?" 라고 방송에서 했어요 = On air, the interviewer asked: "Who can speak Korean?"
(2) Indirect quotation (Reported question : 냐고 )
조사관은 누가 한국어를 말할 수 있냐고 방송에서 했어요 = On air, the interviewer asked who could speak Korean.
On air, the interviewer has asked who can speak Korean.
No, the quotation remains in present tense. Think about it this way:
You) - "What is it?"
Me) - "Sorry, what did you ask?"
You) - "I asked what is it?"
The fact that you asked something happened in the past so that becomes past tense, but the thing that you're asking, i.e. the quotation, remains in the same tense it was originally quoted in.
You are right.
방송 simply means broadcast, emission
It was originally used as you said to mean a transmission of voices and images to the audience at large via radio & TV electromagnetic waves These being invisible to the eyes give the perception of "on-air".
방송에서 하다/방송하다 as used here really should just be interpreted as to make an announcement or to broadcast ...
Need some clarification about the position of 방송에서
• 조사관은 방송에서 누가 한국어를 할 수 있냐고 했어요
= 조사관은 누가 방송에서 한국어를 할 수 있냐고 했어요
= The investigator asked who could speak Korean on air
=> 방송에서 belongs to the subordinate clause
• 방송에서 조사관은 누가 한국어를 할 수 있냐고 했어요
= On air, the investigator asked who could speak Korean
조사관은 누가 한국어를 할 수 있냐고 방송에서 했어요
= The investigator asked on air who could speak Korean
=> 방송에서 is part of the main clause
Generally speaking, Topic and Location nouns are located at the beginning of the sentence. A very literal translation would be, "The investigator, on the air, 'Who can speak Korean?' asked."
You can't put 방송에서 after the subject 누가 because then it's assumed to be part of the question and would literally translate like, "The investigator, 'Who can speak Korean on the air?', asked." You can't put it after 냐고 because that's just not where it goes, although I understand your confusion.
A very general structure for reported speech goes like this: Who said it // Where did they say it // What did they say // How did they say it 조사관은 // 방송에서 // 누가 한국어를 할 수 있 // 냐고 했어요
Thanks John for such prompt reply.
『Generally speaking, Topic and Location nouns are located at the beginning of the sentence.』
Not necessarily, the actual order of a Korean complex sentence is having the subordinate clause leading the main clause as seen in another example:
"노르웨이에서 생선을 많이 먹는다고 || 우리는 들었어요." (We heard || that in Norway they eat a lot of fish)
The word marked by the topic marker, 우리는, still leads the main clause but it does not have to (although for extra emphasis, it can) lead the sentence in its entirety.
This means the present example can actually be rewritten as: "누가 한국어를 할 수 있냐고 || 조사관은 방송에서 했어요." i.e.
냐고 (and for that matters, 다고, 라고, 자고) does not need to be immediately followed by the main verb.
『You can't put 방송에서 after the subject 누가 because then it's assumed to be part of the question.』
Not my intention to do so. But there is no strict rule to what complement may lead a sentence or more specifically a question e.g.
까치가 이 퍼즐을 어떻게 푸는지를 알아요 Magpie knows how to solve this puzzle => 이 퍼즐 belongs to sub-clause (question) while 까치 is subject of main clause
카페에서 우리는 무슨 요리를 사요? What dish do we buy at the cafe? => 카페 (location) heads the question-sentence. This implies that in our given example, "방송에서 누가 한국어를 할 수 있~" (Who can speak Korean on air?) i.e. 방송 could well belong to the sub-clause(?).
Although Korean sentence structure is often referred to as SOV, in practice only the predicate verb seems to matter i.e. OSV works just as well.
This brings back to is my asking that on reading the given example how to distinguish whether 방송에서 belongs to the main clause or subordinate clause i.e.
조사관은 방송에서 누가 한국어를 할 수 있냐고 했어요
= On air, the investigator asked who can speak Korean. Or,
= The investigator asked who can speak Korean on air.