In 2002, the National Geographic Society gave over 300 in-home interviews per country for a selection of nine countries, and gave a geography quiz testing knowledge of current events, international issues, map-reading skills, and world geography.
American young people were ranked eighth out of the nine countries, (up from worst in previous studies), beating Mexico.
Ref, via BBC
In 2006, the study was followed up, but in the USA only, making it interesting but not useful for this answer.