Snakeheads eat anything so offer a variety of foods ranging from insects (caught without bug spray), earthworms, prawn/ shrimp, fish, etc.
If the fish doesn't want dead food you can use a sewing needle and some thread to hang the food from, and jiggle it about in the water. Get a length of cotton thread about 3 foot long and feed it through the eye of the needle. Draw the thread down so it has 2 lengths and tie the ends together so it has a small knot. Feed the needle through the bit of dead fish or prawn and slide it down the length of thread. It should stop on the knot. Then gently lower the food into the tank and move it up and down in front of the fish. The knot should stop the food coming off too easily but if the fish grabs the food, it should be able to easily pull it off the thread.