I was wondering if 닝겐 is pronounced 닌껜, same for 멋대로 as 머때로 and so on? Is the "g" in ㅇ pronounced differently than the "g" in ㄱ?
This word comes from Japanese word にんげん (meaning 'human' [인간]), which is pronounced NEEN-gen. This is how I would basically pronounce 닝겐. Because 닝겐 is a transliteration of Japanese (which has no -ng sound), I would suppress any emphasis on the 이응 받침 (ㅇ on the bottom of the first syllable).