YouTube/BonAppetit chef Molly Baz shows us how the pros do it!
Episode 1: Knives
She's doing some weird flappy motion on purpose visible at the 1:40 mark, like "Hey, I'm going to thin my knife on the edge leading strokes!". It's kind of a miracle that the knife ended up sharp and really a testament to how forgiving sharpening on a stone is. You can see the wicked scratches she left all along the side of the blade at the 3:40 mark since she was basically doing a zero bevel. “15 to 20 degrees”, uh huh sure.