Object menu must be at the center of the object

I am creating a game with isometric camera.
When i click on a object, i must open a menu localized at the center of the object, or at the center of the location where i click
For example, now if i click on the bottom of the cilinder:
(Now i use: viewPosition = Camera.main.ScreenToViewportPoint(Input.mousePosition); to set x and y cordinates of the menu)

I want that A, B menu appear at the center of the cilinder or where i click!

Hello,

This is how to make the button appear when you click the object, put the script on the object you want to be clicked: -

var showMenu : boolean;
var mousePosition : Vector2;
var mouseX : int;
var mouseY : int;

function OnMouseUp(){
	mouseX=Input.mousePosition.x;
	mouseY=Screen.height-Input.mousePosition.y;
	showMenu=!showMenu;
}

function OnGUI(){
	if(showMenu==true){
		if(GUI.Button(Rect(mouseX,mouseY,100,20),"a")){
		
		}
		if(GUI.Button(Rect(mouseX,mouseY+30,100,20),"b")){
		
		}
	}
}

Hope this helps!