What is a possible thesis for an argumentative essay on The Great Gatsby in response to the question of what kind of space Manhattan represents for...

This is a great basis for a thesis for an essay!  As I read through The Great Gatsby(Fitzgerald),what strikes me is that Manhattan represents power and dominance to the males in the novel, which one might think of as the American dream on testosterone. This is true, I think, of Tom Buchanan, Nick Carraway, Gatsby, and even possibly George Wilson.  A thesis statement expressing this, listing the characters as your means of support, would...

This is a great basis for a thesis for an essay!  As I read through The Great Gatsby (Fitzgerald),what strikes me is that Manhattan represents power and dominance to the males in the novel, which one might think of as the American dream on testosterone. This is true, I think, of Tom Buchanan, Nick Carraway, Gatsby, and even possibly George Wilson.  A thesis statement expressing this, listing the characters as your means of support, would get you off to a good and organized start to your content. 

Tom is able to exert his power over his mistress in their Manhattan apartment, to play lord of the manor in a way he cannot at home because Daisy sees him as he truly is, an unintelligent bully.  The scene in which he triumphs against Gatsby and keeps Daisy takes place in the Plaza Hotel. 

Nick is from a well-established midwestern family that has a hardware business. After he returns from World War I, he is restless, wanting something beyond that life.  He plans to make his fortune in bonds, which requires that he succeed in Wall Street, so Manhattan is where the power is.

Gatsby encounters a criminal mentor in a Manhattan restaurant on 42nd Street, and introduces him to Nick.   Meyer Wolfshiem is a gambler who had fixed the 1919 World Series.  Wolfshiem spends his time with Gatsby and Nick fondly reminiscing about a restaurant across the street at which one of his cronies had been gunned down. He represents a certain kind of power and dominance in the criminal world.  Gatsby also tries to make his power grab for Daisy at the Plaza Hotel.  For Gatsby, also a product of the midwest, his dreams of success and power coalesce in Daisy and Manhattan. 

George Wilson never gets to Manhattan, being stuck at the edge of an ash heap, the valley of ashes, on the road to Manhattan. The train passes him up every day, as do those driving into the city. He is shown to be a weak, ineffectual man, powerless, poor, and cuckolded.  Manhattan is not for men like Wilson.

There are other examples of the connection between Manhattan and male power in the novel.  These are a good way to start you thinking, I hope.  I have added a link with photos and discussion of the places in the novel in which New York is featured, which might give you even more ideas.