What is the grading system for cdl knowledge test?

There isn't a single, universally published "grading system" for CDL knowledge tests in the sense of a percentage score. The results are typically presented as a simple pass or fail.

The exact passing score varies slightly depending on the state and the specific class of CDL being tested (Class A, B, or C, and endorsements). The governing authority (usually the state's Department of Motor Vehicles or equivalent) sets the minimum passing score, which is a certain number of correct answers out of the total number of questions. This minimum number isn't typically publicized to the general public.

While you won't see a percentage, understand that you need to answer a significant majority of the questions correctly to pass. Preparation is key!