In addition to knowing the practical elements relevant to your grade, you are required to learn the theory of Taekwon-Do as applicable to your grade for gradings.
This includes:
The interpretations, diagrams and number of movements for all patterns up to and including your grade pattern
The theory behind the application and correct execution of all techniques you have learned
Meaning of all belt colours up to and including your next target grade
Theory of general Taekwon-Do such as its history and etiquette can be found on pages 7-15 in your blue student handbook.
Please see below PDFs links to theory for each grade:
10th Kup White Belt
Red Belt Theory Mock Papers
Black Tag Theory Mock Papers
Always make sure you remember theory from your previous gradings as you may be asked to recall this.