also: なになのか
expression
what is it (that); the meaning of something; what something is about
Used to ask for the essence, meaning, or true nature of something. Often implies a deeper inquiry beyond surface description.
人生とは何なのか、時々考える。
I sometimes wonder what life is all about.
彼が本当に言いたかったことは何なのか、わからなかった。
I couldn't understand what he really meant.
何か is a simple question word meaning 'something' or 'what', while 何なのか asks for the deeper meaning or identity of something.
どういうこと is more casual and asks for an explanation of a situation, whereas 何なのか is more philosophical and asks about the essence.
Combination of 何 (what) + な (attributive form of copula だ) + の (explanatory/emotive particle) + か (question marker). The reading なんなのか is a contraction of なになのか.