similar to "fucking", "damn", "shit" correct word is 좆나 (좆 means dick, 나 or 나게 can be translated "seem, feel, it feels like") but many koreans use 존나, 졸라. ex) 너 존나 짜증나. damn, you piss me off. 이거 존나 좋아! it's fuckin' good! yeah... it's a slang for sure

Oh, it is really embarrassing expression. it is a swearing that refer something of men's. You shouldn't use this expression, though lots of Korean students use it without knowing what it means. Definitely it is a slang.