Here is JavaScript sample to use GeoMap with Leaflet JavaScript library.
http://locate.pitneybowes.com/docs/location-intelligence/v1/en/index.html#GeoMap/Code%20Samples/code_sample_javascript.html
You can use below snipped to get a lat/lon when user clicks on the map.
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);
});