Your friend David tries to write down everything the professor says because he has difficulty ...

I would tell David that although it is important to have good notes, it is not necessary to write down everything. Coming to class prepared, having read the material ahead of time, will make it easier to take notes. He should look for instructor clues about what is important. Sometimes the professor will announce that a topic is important, but this is not always the case. Information is typically important if the professor spends a lot of time on a topic, repeats information, speaks more loudly or passionately, or displays the information visually. These clues will help you discern what is most important. You can also meet with the professor after class to confirm that you captured the key points. After class, you can also fill in information as you read the textbook.

Thank you very much