- Use paper. I could annotate printed PPT slides with the whitespace on 4 per page, but sometimes would overflow onto the (blank) reverse side. Computers have too many distracting notifications.
- Write down questions with a big (?) and ask them at an appropriate time. Professors care much more about that than you think, in Western education systems (don't get me started about my ill-fated Ph.D. attempt in Korea).
- Use coloured pens. If you think this looks too feminine or gay, get over yourself. It's SO much easier to quickly speed-read and study once you're doing this. I would use red for formulae, green/pink for definitions, black for examples, pencil for diagrams, blue for everything else.
Example: https://www.flickr.com/photos/150180606@N08/49613268401/in/d...