Final answer:
One speculation about Gatsby made by guests at his party is that he is a bootlegger, but this is a misconception. Other speculations include him being a German spy and a war hero.
Step-by-step explanation:
One of the speculations made by guests at Gatsby's party is that he is a bootlegger. However, it is important to note that this is a misconception about Gatsby. While he did make his fortune through illegal means, primarily by selling alcohol during the Prohibition era, he is not actually a bootlegger. Gatsby's wealth comes from his involvement in organized crime, specifically through his connections with the underground world of gambling and smuggling.
Another speculation made by guests is that Gatsby is a German spy. This rumor arises due to his mysterious past and the fact that he throws extravagant parties without seemingly having a legitimate source of income. However, this is simply a baseless assumption made by the guests and has no factual basis.
Lastly, guests also speculate that Gatsby is a war hero. This speculation is not entirely untrue, as Gatsby did serve in World War I, but he was not a hero in the traditional sense. While he did receive medals for his service, his military career was somewhat questionable, involving rumors of him being involved in illegal activities even during the war.