Noun and する verb
じんもん
警察は関係者全員を尋問しました。
The police questioned everyone who was involved.
When you inquire about a problem, you tend to do questioning about said problem. Why is it like this? What happened? Is it bigger than a breadbox?
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.