Knowledge gives us facts. The conclusions we draw from those facts involve reasoning.  Our reasoning may be correct or it may be faulty. There is a good chance that it will be faulty if we do not apply the principles of correct reasoning. Grade seven or eight is the generally recommended time for beginning the study of logic.

The  study of the structure of correct reasoning (Formal Logic) is considered in Traditional Logic Book I, An Introduction to Formal Logic and Traditional Logic Book II, Advanced Formal Logic.  The rules of formal logic as applied to practical situations (material logic) are treated in The Ancient Art of Thinking - Material Logic, Book I - A Traditional Approach to Thinking Skills. Another title which looks at very practical application of thinking skills is Half Truths: What's Right (and What's Wrong) with the Clichés You and I Live By.

Closely related to this study are the books which you will find listed in the category of Wisdom / Natural Law.