According to the official GMAT site (MBA.com), the verbal section measures your ability to:
- read and comprehend written material,
- reason and evaluate arguments, and
- correct written material to conform to standard written English.

More info at: https://www.mba.com/the-gmat/test-struct ... ction.aspx

For the math section ...
Problem-Solving questions are designed to test:
- Basic mathematical skills,
- Understanding of elementary mathematical concepts, and
- The ability to reason quantitatively and solve quantitative problems.

Data-Sufficiency questions are designed to measure your ability to:
- Analyze a quantitative problem,
- Recognize which information is relevant, and
- Determine at what point there is sufficient information to solve a problem.

More info at: https://www.mba.com/the-gmat/test-struct ... ction.aspx

I hope that helps.

Cheers,
Brent