C# two double quotes

One way is to escape the quotes:

var greeting = "\"Hello World\"";

Escape them:

Console.WriteLine("\"Hello world\"");

Console.WriteLine("\"\"Hello world\"\"");

The backslash ('\') character precedes any 'special' character that would otherwise be interpreted as your code instead of as part of the string to be output. It's a way of telling the compiler to treat it as a character part of a string as opposed to a character that would otherwise have some sort of purpose in the C# language.