Which key is denoted by a ^ on a Macbook?
This is ^ CTRL key (or Control on some keyboards). 

Here'e more info on Apple website.


  Mac menus and keyboards often use symbols for certain keys, including the modifier keys:
  
  
  Command ⌘
  Shift ⇧
  Option ⌥
  Control ⌃
  Caps Lock ⇪
  Fn