How to add double quotes to a string that is inside a variable?

You need to escape them by doubling them (verbatim string literal):

string str = @"""How to add doublequotes""";

Or with a normal string literal you escape them with a \:

string str = "\"How to add doublequotes\"";

So you are essentially asking how to store doublequotes within a string variable? Two solutions for that:

var string1 = @"""inside quotes""";
var string2 = "\"inside quotes\"";

In order to perhaps make it a bit more clear what happens:

var string1 = @"before ""inside"" after";
var string2 = "before \"inside\" after";

If I understand your question properly, maybe you can try this:

string title = string.Format("<div>\"{0}\"</div>", "some text");