Question

What figurative language is this? ..—> Lee always get 100% on his test ;he knows absolutely everything there is to know about math

Answer 1

The sentence uses figurative language called hyperbole.

Hyperbole is a figurative language technique that uses exaggeration to create a strong. Of course, Lee doesn't know everything about math, but the use of  hyperbole expresses that Lee knows a great deal of math.  

Answer 2

The figurative language used in this expression is IDIOM, commonly used to refer to a person who knows very much about everything. In this case it refers to a very good student that gets the better grades in his exams. Anyway, idioms are expressions that usually cannot be explained word by word, they have to be taken as a whole.