I received a reply from the Guam Hotel and Restaurant Association:
Hafa Adai Nadja:
You will need to obtain an Alcohol Beverage Control (ABC) license in order to serve and sell liquor as a bartender. You will have to take a class to qualify for it. There is also a requirement to obtain a health certificate. Your employer will have to assist you in obtaining both of these government requirements.
DAVID B. TYDINGCO