You can perform one of three tests to determine the sharpness of your kitchen knife.  The first option includes folding a piece of paper in half and trying running the blade through the paper. If the knife easily slices through, it is sharp enough for use. If the knife struggles through slicing the paper, you should consider using your electric knife sharpener.  Secondly, you can try slicing a tomato with your knife. If the blade easily slices through the skin of the tomato, the blade is perfectly sharp. However, if the blade crushes the skin, leaving a mess of tomato juice on the cutting board, you know that the knife needs to be sharpened.  Finally, attempt cutting an onion with your knife. If the knife can easily cut through the outer casing of the onion, it's in good shape. On the other hand, if the blade can't cut through the outside of the onion or struggles to do so, it needs a good sharpening.