From what I know, か is the standard question particle, and is used universally by everyone.
の is primarily used by women.
I haven't heard of のか, so I looked it up and here is your answer. Judging from the first result, I don't think のか is a question particle.
か isn't usually emphatic but its more masculine variant かい is.
の can be emphatic, but when I use it in writing, to be on the safe side, I use it with わ, the feminine emphatic particle.
のか is definitely empathic, as
It reflects lamentation on the preceding statement. (From the page in the link)
From all of this, I can say that anyone can say 「もう宿題【しゅくだい】を終【お】えたか？」, but 「もう宿題を終えたの？」is more likely to be said by females. 「もう宿題を終えたのか？」doesn't make sense, either in usage or translation. Personally I recommend 「もう宿題を終えたかよ？」or 「もう宿題を終えたのわ？」to emphasize the もう (already).
You also have to consider regional variations. と and け (Satsugu dialect) is used as the question particle in the Kyushu dialect, け and か in the Kansai dialect.
Not that you may be interested, but a person who speaks in Kyushu dialect would say 「も宿題【しゅくで】を終【お】えっけだい？」.
I am not very experienced in Japanese or the Kyushu or Kansai dialects (I learnt Kyushu dialect using Wikipedia only), so please correct me if I have made a mistake.