A elephant can eat all dayif it wants to. An African elephant in the wild can eat about 770 pounds of food in a day. A elephant in the zoo can only eat about 150. An asiatic elephant can eat about 650 pounds in a day.
People can eat almost anything that does not kill and eat them first, (including other humans), so I am sure that it is possible to kill, cook and eat an elephant. I have no idea how an elephant would taste.