How you can draw a line on Google Maps through KML?

You can load KML (with points, lines, polygons, etc.) either directly on google Maps website or via the google Maps API.

google Maps supports KML via the google Maps API. See related links below for details.

The classic google Maps interface supports KML via the search query. Just enter a URL to a KML file in search box and google Maps will load the KML and render on the map, but this only works in the classic google Maps interface.