How to launch the onscreen Accessibility Keyboard with a keyboard shortcut too?
There is no built-in way to use a keyboard shortcut to display or hide the accessibility keyboard. 

I'm understanding your question to only be about showing &amp; hiding the accessibility keyboard with a keyboard shortcut and not about how to use that keyboard or any other accessibility feature.  If that's not correct, please edit your question or add a comment to clarify.

One-sentence answers are usually not very good but in this case there's not much more to add that would improve the answer.