Noun, な adjective, and の adjective
ほんき
いつになったら、本気を出すんですか。
How soon before you make a serious effort?
ついにコウイチが本気を出してきた。
Koichi is finally getting serious.
私があの男の頭の毛をむしったなんて、本気で思ってないよね？少しは私を信用してよ。
You didn’t seriously think I pulled that guy’s hair out, did you? Give me some credit.
What is book energy? It is energy you put into reading - it is your studies! In order to have book energy, though, you have to be very serious.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.