Using Leaflet Js, is it possible to know the onclick location of a Marker (ignore anchor point)?

On one hand: whenever Leaflet handles a mouse (or touch) event, you can access the original DOM event in the originalEvent property of the event.

On the other hand: Given a mouse (or touch) DOM event, Leaflet can magically translate its clientX and clientY properties into an instance of L.LatLng by using map.mouseEventToLatLng().

Combine these two things together, and you can have something like:

marker.on('click', function(ev){
  var latlng = map.mouseEventToLatLng(ev.originalEvent);
  console.log(latlng.lat + ', ' + latlng.lng);
});

Check Leaflet's documentation for the other conversion methods, as they might prove useful.

You always can retrieve the coordinates from the Leaflet object map. You can use something like this:

map.on('click', function(e){
  var coord = e.latlng;
  var lat = coord.lat;
  var lng = coord.lng;
  console.log("You clicked the map at latitude: " + lat + " and longitude: " + lng);
  });

Here you have a working example.