What’s the shortcut for “Edit All in Scope” in Xcode?
Menu: Editor -> Edit All In Scope (also shows key binding)
Keyboard Shortcut: Control-Command-E
If you want you can change this key binding on Preferences -> Key Bindings -> search for "Edit all in scope".
EDIT: In Xcode 9, you may want to instead use the fabulous new "Rename…" functionality, which works across classes, also renames files and comments, and gives you a neat preview. As of beta 2, this does not have a default keyboard shortcut, but you can easily give it one.
Press Cmd-Ctrl-E
to edit all in scope