How to get the Latitude and Longitude from google maps

I'm not sure your question is entirely clear

How to get the Lat & Long OF WHAT ??? - Your position, the position of some other entity like a building or landmark, or a marker that was added to the map.

If you're after 'you're own position', depending on what sort of device you're doing this on, why not read it directly from the devices GPS sensors ? (eg iPhone, Android) .. because if you're looking at a Google map on these devices, showing 'your position' on the map, thats one way they know where you are to be able to plot it ...

If you're looking for 'some other Lat/Long', then you're going to need to elaborate a bit more