I did it this way:
//Create symbol on stage.
//The number 1 indicates the position in the list
//of the symbol instances on the stage,
//like the one you see in the right panel called "Elements".
//Use it to set the z-index (position elements in front or in background).
var myNewSymbol = sym.createChildSymbol("myNewSymbol", "Stage", 1);
var x = e.pageX;
var y = e.pageY;
// I wanted position to be in percentage
var bodyHeight = $(window).height();
var bodyWidth = $(window).width();
var xPercent = 100 * x / bodyWidth;
var yPercent = 100 * y / bodyHeight;
//Set the position
myNewSymbol.getSymbolElement().css("position", "absolute");
myNewSymbol.getSymbolElement().css("left", xPercent + "%");
myNewSymbol.getSymbolElement().css("top", yPercent + "%");