just trying to make sure i understand the card so that i use it properly, do i need to have a Deathtrooper card in play to get the die or do i get a die everytime i activate Krennic then either resolve it or wait to remove it?

It basically acts as his dice, you roll it out when you activate him as long as you control the battlefield. You don't need to have a death trooper in play.

According to the latest RRG, you take a Deathtrooper die from your Set Aside zone, and roll it into play when Krennic is activated. If there is no die in your Set Aside zone, Krennic does nothing.

That means you can have a spare Deathtrooper die set aside, and use that die for his ability. Or, if a Deathtrooper you're controlling is defeated, you can start rolling its die in from the Set Aside zone with Krennic.

All his ability requires is that the necessary die be in the necessary zone.