To earn the trophy that's called "Nom Nom Nom!", you have to eat an Uruk Captain with a Wretched Graug. It's pretty simple!
First off, find a Worm (an Uruk with a green symbol) or a group of slaves, one of them also with a green symbol on it). From there, either dominate the Worm or speak with the slave to gain Intel on your chosen captain. Alternatively, you can simply find a random Captain on the Sauron's Army screen and target him as well.
Once you gain the information you need for that Captain, it's time to find a Wretched Graug. Fast travel to the tower that's all the way to the right of Num, where you start out. Walk a little bit forward and use Wraith Vision (by pressing
) to locate a Graug Bait that's hanging underneath a bridge. I recommend using your bow and arrow to shoot the bait and wait at least ten seconds for the Wretched Graug to appear. Once he does, use the Shadow Mount technique to jump on top of him and dominate the beast.
Now that he is under your command, find your Captain on the map and target him. Then follow your mini-map, which is located on the lower-left corner of the gameplay screen, and hunt him down. Once you reach that area, use Wraith Vision and look around until you see a red uruk with an R3 symbol above his head. Press down the
and he will be targeted on the gameplay screen. From there, maneuver your Graug until you are close enough to the Captain and press
to have the Graug swipe the Captain off the ground and then watch the quick cutscene as the Graug lifts the poor uruk Captain into the air and bites off his head.
Once he's eliminated, the trophy should unlock right away! If you need a visual aid, this should be helpful. I've attached a video guide for this specific trophy. All credit goes to Solus Sicarius Guides for the video upload. It's a short video, but it gives you the right idea on how to get the job done for the trophy.
Have fun, good luck, and happy hunting!