Is the laptop's power adapter output negative terminal grounded?
If the laptop is not grounded, is it safe?


Some laptop adapters don't have an earth pin and therefore they can never have a grounded output. It's not a problem providing that the insulation and clearance/creepage distances inside the adapter are adequate. 

If a laptop uses a grounded adapter and the adapter is unplugged from the laptop then, the laptop isn't grounded - it's clearly safe in this scenario and, just as safe as when plugged into a properly designed and manufactured adapter that doesn't need an earth pin in the AC plug.