See Pet Debuffs

To my knowledge there is no way to see your pet's debuffs on the default pet frame. After much tinkering I was able to accomplish this by setting my pet as the focus frame and hiding the original pet frame, all but the happiness icon. I can then use the in game edit mode to move my focus frame to where i want it and place the happiness indicator near by. This allows me to recreate the desired result of being able to see the debuffs on my pet. 

type /spd in the chat box to unlock and relock pet happiness indicator, hover over icon while unlocked and use mouse wheel to resize. 

I also place the following macro on my action bar

/focus [@pet,exists]

I press it once i log into the game/anytime my pet focus frame disappears, ie at a load screen or if I dismissed my pet and resummoned a new one. 

Works for Hunters and Warlocks too!