There is no penalty for incorrect responses on the GRE because reported scores are based on the number of correct responses to all the questions. The Verbal Reasoning and Quantitative Reasoning measures are section-level adaptive which means that the computer selects the second section of a measure based on your performance on the first section. Poor responses across a section of the exam result in an easier set of questions next. Right answers to difficult questions are worth more than right answers to easy questions. Within each section, all questions contribute equally to the final score.
The total raw score is the number of questions you answered correctly. The raw score is converted to a scaled score that accounts for section difficulty.
You will not be penalized for wrong guesses, but try your best to make educated guesses. Narrow down the choices as best you can. If you can eliminate 1 or 2 responses, your chances of answering a question correctly improves. Eliminate obvious wrong answers and then go with your gut. Do not spend a lot of time on this - respond and move on to new questions that you may be able to easily answer.
Because only correct answers contribute to your total score, guess, if needed.