I recommend that he learn to use a whetstone if he wants to sharpen it himself. I dont know anything about that sharpener, but it looks like it could have some problems. Not all knives are created equal and the angle of the edge can vary quite a bit based on the type of knife and what you are using it for. For example, a boning knife and a chefs knife will usually have different edge angles as the chefs knife needs to be more durable. I have a business in town that will sharpen my knives to the specifications that I want for about $10/knife. You could always look up knife sharpening services in your area and have it sharpened when it needs it. Also, he needs to learn to properly maintain and hone the knife for edge longevity. Hope that helps and good luck!

There are plenty of good videos on YouTube to learn. Grab a POS knife from walmart and at least 3 different grit stones and start trying it out. It takes getting used to but your muscles will get used to it and hold the angle better as you go. Youtubers will often recommend stones of varying prices. I stopped bothering as I have a local place that does what I need, but it can be very soothing to sharpen your own knives