Try this. This is a list of the apps a person has that are persistent in the dock. What I've basically done is use system events to read the plist file into an applescript record in the pListItems variable. Then I can use applescript techniques to access the lists and records inside of pListItems.
There's lots of information in com.apple.dock so you can look at the pListItems variable and work your way through it to pull out whatever you need. For example you might want the "|bundle-identifier|" instead of the "|file-label|". Good luck.
set plistpath to (path to preferences folder as text) & "com.apple.dock.plist"
tell application "System Events"
set plistContents to contents of property list file plistpath
set pListItems to value of plistContents
end tell
set persistentAppsList to |persistent-apps| of pListItems
set dockAppsList to {}
repeat with thisRecord in persistentAppsList
set end of dockAppsList to |file-label| of |tile-data| of thisRecord
end repeat
return dockAppsList