$ajax get data in code behind problem

 I use this:

type: "POST",
url: "mywebpage.aspx,
data:{Arg:args2}
Does anyone know how can i get value of arg from sever side(code behind)?
i dont know how to fatch data when data put inside
{}, " data:{Arg:args2} "
Can i still use Request.QueryString("Arg") function? or  Request("Arg")
thanks

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