This is the 3731st most frequent Japanese word.
こん
"こん" in Japanese can mean "this" or "now," depending on context, or refer to the color "dark/navy blue."
In this sentence, '今' (kon) is used as a prefix to indicate 'this or the current,' referring to the night in question (今夜 - konya).
今夜、星がきれいに見えるでしょう。
Tonight, the stars will likely be beautiful.
Here, 'この' (kon) is part of the word 'konno' meaning 'this,' used to specify the particular book being referred to.
この本はとても面白いです。
This book is very interesting.
In this context, '混' (kon) appears within the word '混雑' (konnzatsu), meaning 'crowded,' where 'kon' refers to 'mixed' or 'in a state of mixture.'