where are the zero point of Northing and easting in the world?

Answer 1

0 degrees latitude, 0 degrees longitude. It's a marker buoy in the Atlantic Ocean at present.
Of course, in Surveying and GPS coordinate geometry, the point is usually 'assumed' as 5000.000+5000.000, then rotated and translated into whatever local or area map assignment is applicable.

Answer 2

The zero point for calculating latitude (north-south position) is the equator.

The zero point for calculating longitude (east-west position) is Greenwich in Britain.