You should add the click listener on marker will give you the position of marker.
//Add listener
google.maps.event.addListener(marker, "click", function (event) {
var latitude = event.latLng.lat();
var longitude = event.latLng.lng();
console.log( latitude + ', ' + longitude );
}); //end addListener
Edit:
You need something like this
//Add listener
google.maps.event.addListener(marker, "click", function (event) {
var latitude = event.latLng.lat();
var longitude = event.latLng.lng();
console.log( latitude + ', ' + longitude );
radius = new google.maps.Circle({map: map,
radius: 100,
center: event.latLng,
fillColor: '#777',
fillOpacity: 0.1,
strokeColor: '#AA0000',
strokeOpacity: 0.8,
strokeWeight: 2,
draggable: true, // Dragable
editable: true // Resizable
});
// Center of map
map.panTo(new google.maps.LatLng(latitude,longitude));
}); //end addListener