What is the easiest way to go to Shanghai Disneyland from Hong Kong?

Well, you need to fly to SH first.
If you will arrive at Pudong Airport, you can take the Disney line directly there, which is available from 8:00 to 19:30.

If you arrive at Hongqiao Airport, you can take metro line 10 and transfer to line 11 at Jiao Tong University, and then get off at Disney from Exit 4, you will see it.