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. けん gets changed to げん, though, so don't let that ruin your mood.
Koichi gets in a good mood for three o'clock snack time, every day like clockwork.
What kind of mood is mom in today?
"Her mood's terrible in the morning." "Yeah don’t I know it!"