I don’t actually understand your example so I use a different one
Asssuming you want to list the root directory on your external volume “my external HD”
you will type in Terminal
ls "/Volumes/my external HD"
In AppleScript you can either use single quotes
do shell script "ls '/Volumes/my external HD'"
or escape the double quotes (with a backslash, which also must be escaped with a backslash)
do shell script "ls \\"/Volumes/my external HD\\""
or just escape the space characters
do shell script "ls /Volumes/my\\ external\\ HD"
or use the built-in quoted form keywords
set myVol to "/Volumes/my external HD"
do shell script "ls " & quoted form of myVol