Zener Diode Identification/Replacement
Yes, you can use a similar Zener:


the same or higher power
the same breakdown voltage


If you can't identify this diode, it would be a good idea to take it out and measure its breakdown voltage.


  It is reverse biased across 28V Input and GND


If this is what you mean:


Source: HyperPhysics

Then the breakdown voltage is VZ