Desert Nagas is an intermediate grind-zone. Naga mobs are primarily fought for quest-related reasons and also used as a grind spot early on. The xp here is decent but nothing special. With that being said, this spot is decent early on, but you should focus on questing until you reach level 56 - once level 56, you can grind Polly's for better, more profitable rewards. Polly's is also one of the best spots in the game for xp. If you reach level 56 but still cant kill pollys Nagas will do until then.
Desert Nagas located right to the left of Sand Grain in the desert; The desert is located North of Altinova, the fourth major city in Black Desert.