He is located at the top of Camp Orqawanga, which is situated southeast of Pluckmuckel and west of the Haunted Forest. There are a lot of enemies besides Sergeant Orque in the Camp, so try to kill everyone of them before you attack him. Although they probably won't attack you during the fight, you don't want to take the chance.
One of the first storyline bosses you'll face. He is level 16 and can take a punch. Like all enemies, if you leave the area, he will regenerate health and since he can hurt you somewhat fast, I suggest you have a lot of health potions on hand. They immediately give you health while the food is a timed replenishment process. Every so often he takes out a trumpet and calls out several level four foot soldiers. They're easy, but pests, so take them out as soon as he calls them!
The main thing is, to just keep hitting him with everything you've got and when you're health drops low, instantly give yourself a health potion. He is rather slow and has no ranged attack, so if you have no health potion but plenty of food, grab a bite and run around in his general area, but stay in his general area so he keeps chasing you. If he turns back and walks away, his health will regenerate to 100%.