Is there a skill or is it even possible to jump while using an attack as a bowman?

So how does this work then? Do I have to press the button for jumping and my atk at the same time?

Pretty much... It's *really* dependent on your keyboard though. On mine, I can easily jumpshoot strafe & iron arrow, but I can't jumpshoot a regular attack if my life depended on it. If I swap around the keys in my config, then I can easily do it with regular attacks.

You might have to experiment a little until you get the hang of it. I purposely put my attack keys on the ones where I can jumpshoot easily.