To sharpen a knife on a whetstone, start by soaking the stone in water. Place the knife on the stone at the around 20° angle. Slowly draw the knife across the stone in a smooth, consistent motion, moving from the heel to the tip. Repeat this process several times, flipping the knife to sharpen both sides. Check the edge regularly by riffling your thumb across the edge and feeling the burr. Once you've achieved your desired level of sharpness, hone the edge with light strokes on each side to remove any micro-scratches and create a razor-sharp finish.