Microsoft Word notebook layout - insert equation?
One workaround is to assign a keyboard shortcut to inserting an equation.  This only gets you the ability to type an equation, not use the Equation Tools in the Ribbon.  You can also get the Equation Editor to open in a separate window via assigning a keyboard shortcut.  If this workaround is sufficient for you, it's fully documented here. 

There is a third-party application called MathType for editing equations, and it works with many applications including Word:Mac.  If you know TeX/LaTeX, you can type that into MathType and it works magically.  However ... it doesn't work in the Notebook Layout View either.  I asked them about it via Twitter, and they said this:


  No, but only because of the types of items Word allows to be inserted
  in Notebook Layout View. No editable objects, only static.


Don't forget to tell Microsoft that you want the full power of the Equation Editor (or MathType) in Word:Mac.  In Word's Help menu, there's a "Send Feedback About Word" link.  Tell them what you're doing and why this matters to you.