Advantage Testing GMAT Q&A

No, you should not skip any questions on the GMAT. Both the Quantitative and Verbal sections are computer-adaptive—the computer will present questions of varying difficulty depending on your prior responses. Therefore, you cannot skip difficult questions. In addition, note that questions cannot be returned to after they are answered. 

There is a severe penalty for not finishing the test, so be sure to answer every question in a timely fashion. You should always keep track of time remaining so that if you have unanswered questions remaining when your time is almost up, you can complete the section with random guessing in the last minute or so.