Bind a key, and copy text from whatever your mouse is hovering over.
Chatframes, QuestText, Menus whatever.
You can bind a key from the blizzard key bindings configuration menu.
The following slash commands are supported:
/cpyt <Name of Frame>
This is mostly used for the chatframes, eg.
you can bind keys to copy the frame that your mouse pointer is over, or the game tooltip (since you cant mouse over it).
I suppose you could also use: /cpyt GameToolTip