Applescript double quotes issue

You don't need to use either a do shell script or osascript to control volume in AppleScript. Just type:

set volume output volume 51 -- 51%.

See the set volume command usage in the AppleScript Language Guide.

In AppleScript, and in particular, using osascript in a do shell script invocation, the syntax is:

do shell script "osascript -e 'set volume output volume 51'"

You can reference this 2013 post that offers more osascript volume options. Just use the quoting format above. I tested some of these article entries and they still work in El Capitan 10.11.6.

I do not think you need to do anything fancy with the quotes.

On the command line (in the application Terminal) you can enter:

sudo osascript -e "set Volume 5"

then you have to enter your admin password

I have not been able to get this to work in AppleScript