Does Google Maps have info of the level above sea of ground?
If so, how can I get it?
Altitude is elevation above sea level. You can use the Google Elevation API to integrate this information into a map.
What Can You Do With the Elevation API? The Elevation API provides elevation data for all locations on the surface of the earth, including depth locations on the ocean floor (which return negative values). In those cases where Google does not possess exact elevation measurements at the precise location you request, the service will interpolate and return an averaged value using the four nearest locations.
There are a number of services online such as this VeloRoutes Elevation map that allow you to search and find the elevation of a location.
Google Maps shows altitude data when searching for walking or cycling routes.
If your purpose is to check out the difficulty of a route, or check the altitude difference between two points it's quite straight away.