Try this:
tell application "Evernote"
if (count of selection) is equal to 1 then
set originalTitle to title of item 1 of (selection as list)
set newTitle to "Evernote-" & originalTitle
end if
end tell
This gives you two variables: one with the original title and one with the prepended title. You can use both of them later in your script. If you want to change the title of the note, include this line
set title of item 1 of (selection as list) to newTitle
right after newTitle
is defined.