(Kun) reading is used when the kanji alone is used. But if you were to see a bunch of kanji's put together such as a compound like 最善、uses the ONYOMI reading. If the word is
If it is the (KUN) reading, then it would look like this such as 皆さん、the kanji 皆 means everyone in which the (KUN) reading is みな。So, it is chinese or (ON) when the kanji's are used in a compound structure or combined with other kanji's and (KUN) when it is used alone as in okurigama.