"Wonder City" or "Wonder City of the World" has been applied to many cities and has, sometimes, been the nickname of New York City. The nickname was popular in the early 1900s and during the 1939-40 World's Fair.

18 November 1883, Atlanta Constitution, pg. 2:
FATHER RYAN ON NEW YORK.
From a Recent Letter by Him to the New Orleans Times Democrat.

I came directly to Kansas City, Missouri, from New York, the wonder city of the world.

28 July 1906, Atlanta Constitution, pg. 11 ad:
NEW YORK,
The Wonder City of the World.
(...)
"NEW YORK
(The Monthly Visitors to New York)
FOR AUGUST.
"New York" is a beautiful illustrated publication, which proves New York's greatness as a summer resort "by word and feature" as no other publication ever did.

13 October 1907, New York Times, "The Story of the Supremacy of New York City," pg. SM6:
Passing from these generalities to a more detailed survey of the metropois -- a city not half-known to most New Yorkers -- facts are met with at every turn which contribute to make this the wonder city of the world.

9 January 1930, New York Times, pg. 52:
Smuts hails New York as wonder city of the world.

31 July 1938, New York Times, pg. 117:
The "Wonder City"
of the World's Fair

26 October 1940, Chicago Defender, pg. 20:
On his first visit to the Wonder City of the world Rene is making the acquaintance of Tin Pan Alley the Broadway street where all of the nation's popular hits are written.

30 October 1945, New York Sun, pg. 20 ad:
NEW YORK

Wonder City
of the World
(...)
OHRBACH'S

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