Is the の[か] in my sentence a 準体言助詞 の[か]?

Question

こんな訓練が何の役に立つのか不思議だったが、アインが言うにはバランス感覚は射撃の要になるらしい。

I hypothesize that the のか in question is a nominalizing の followed by a questioning か, as its preceded by the verb/expression 役に立つ. This verb-preceding-の-nominalization is explained and exemplified in this answer I found while researching data to verify my hypothesis. However, my knowledge of のか is still lacking as far as I'm aware, so I'd like a second opinion to verify or disprove my hypothesis as to what the above sentence's のか is.

(If the wording of this question is vastly different from my previous ones, its because I am finally taking a grammar course where I'm learning how to approach words and questions about them as a linguist or as a language student would.)

Answer 1

This の is best known to learners as an explanatory-no. The か right after it is a questioning particle, which in this case is forming an embedded question. When の and か are used together, it sounds like you are seeking clarification. If you already know how to make a question using ～のですか, this のか is basically the same except that です is not used because it's in the middle of a sentence. Broadly speaking, this の is a kind of a nominalizer, too (you can think this の turns "to run" to "that one runs"), but it may be better to think this の as a distinct particle.

準体助詞 is the name of a word class which this の belongs to in the Japanese "国語文法" (the grammar taught at Japanese classes to native Japanese students). If you are still learning Japanese grammar, I suggest you master the basics of your Japanese-as-a-second-language textbooks first, and revisit this term later.