a matter that isHere, 일 means “matter” or “thing,” and 인 is the form of 이다 used before another expression. It commonly appears in phrases like 일인 것 같아 (“seems to be a matter”) or 일인 거야 (“is a matter”).
KO: 그건 내가 해결해야 할 일인 것 같아.
EN: I think that's something I need to take care of.