Send him a meeting invite. If your topic is small, just ask for 15 minutes. If long, ask for 30 or 60 or whatever. A good time to ask for is 5PM. Copy his assistant, if he has one. If he is not available, he will just counter. But just take action and send the actual invite.
Face to face is best (location "your office"), phone is next best (or even better Skype/Zoom, etc. now that even the geezers has been forced to learn them). But phone is still fine, especially if he doesn't want to do video. Don't ask for a chat meeting...that is bizarre and distracting. IF he volunteers that, then fine, take it.
You don't need a document, but have a simple outline (can be in the meeting invite description field) for breaking down the topics and making sure key questions are asked. (You can allow the meeting to be natural and back and forth, but having an outline will help make sure the time is not wasted.)