야식 = midnight meal
It's probably with a question mark "야식인갓? (야식인가?)" = "Wow, a night-meal is about to be served?"
That 'ㅅ' attached is just pun, and nobody speaks that way. If you do, people will stare at you with their eyes shouting "WTF".
And that's why I disadvise from reading webtoons for language learning.