How many kilowatts/hour for a city like New York requires a day?

Answer 1

From Consolidated Edison (the electric provider for NYC):
On August 2, 2006, we set a record for peak electricity demand, reaching 13,141 megawatts at 5 p.m., topping the record of 13,103 megawatts the company set on August 1.

(One megawatt is enough electricity to power approximately 1,000 homes.)

Those are peak numbers, so you're talking 13,103,000 kW for an hour at peak demand.

Con Edison's site says they provide 55 billion kilowatt hours annually, which is an average of 150 million kilowatt hours per day.