「二人とも、またこんなところで練習をしていたのかい？」
「仕方ないだろ。エレンの奴、一向に成功しねえんだから。カレンの方は優秀だってのに、なんで姉妹でここまで差が出るもんかね」
What would be the usage or nuance of the bold もんかね? How is it different from just のか? I know ものか can mean “definitely not” or “impossible”, but this example seems to have a different nuance.
This もの/もん is the same as もの/もん you have asked before:
The difference is that the question marker か is used instead of だ. In this case, the added nuance is "is that the way sisters work (in general)?", etc. The speaker is talking not only about "these sisters" but also about "sisters in general".
なんで姉妹でここまで差が出るもんかね
I wonder why (in general) there's this much difference between two sisters.
By the way, I think ものか/もんか meaning "I will never ～" is in the same vein. It implies it's not a "one-time no" but "always impossible in any similar situation".
Ahhh...I can see how this is confusing.
The nuance is that you gripe the unfairness of the world. Here in this example, you got two sisters, one with utter success and the other, a failure. One remarks on how unfair it is.
GIve me your translation of the above example and I can point where you might have gone off the rails.
Similar to the other responses, I would translate it as more rhetorical-sounding - " How can two sisters be so different?!" This adds a tone of incredulity to the statement. Using "why" in this situation, although logical, just sounds awkward.
