How should you approach your adviser and tell him that he has a communication problem
I would advise you to approach him on a different base than he has a communication problem, namely on the base that you have a problem with his way of communication. Note the slight shift.

Phrasing it that way eliminates the problem that you may accuse him of something or even offend him. For example, you would not say "your handwriting is poor" but "I have a hard time to read your handwriting and it costs me a lot of time to read it". Also, you would not say "your slides are unclear" but "I do not get the main idea from the slides and would find it helpful if [...]". Finally, instead of "your notation is unclear" you would say that "I consistently get confused since the book X uses the notation Y while you use Z".