What is a grade 66.8 on GPA?

A GPA is usually calculated on a 4.0 scale (or sometimes a 5.0 scale). There's no direct conversion from a grade of "66.8" to a GPA without knowing the grading system used. A 66.8 suggests a failing grade in most standard grading systems. It's likely well below a 0.0 GPA on a 4.0 scale. You'd need to know the specific grading scale used to convert it accurately.