Currently Korean airports do not regulate those things for transit passengers (at least last time I checked), but things change very often these days, so I do recommend to buy duty free liquid in ICN airport, or on inflight duty free shop on ICN-PNH. In case LAX-ICN flight is delayed so that no time to buy things in ICN, pre-order inflight duty free will be the best choice for liquids (because things your visitor will buy are usually fixed)