What cognitive functions are impaired with alcohol?

All of them... ...To varying degrees. Sadly, insight and judgment are among the first to go, so that the first to disappear are inhibitions against consuming more alcohol, and other high-risk activities.
All of them. Alcohol starts working on the pre-frontal cortex, which is where most of our inhibitions are, so we become looser and disinhibited. As it works its way downward, it affects judgement, memory and decision making, eventually affecting balance, coordination, hand-eye coordination, visual tracking, reflex times. One or two drinks causes mild disinhibition and relaxation; beyond that, you get the rest.