"Eine Einführung in die OpenGL Shading Language"
I don't know if that book is really helpful, you want to learn writing
HLSL shaders in A8 and yes, there are some special things to consider concerning acknex.
I recommend that you do the
shader workshop, watch
Slin's German shader tutorial (that's how I've learned shader programming, thanks again, Slin!) and repeat.
I suggest that you start with postprocessing shaders, for example take the emboss shader from the online workshop and experiment with it. Then learn a few basic things such as how information is transmitted from the engine to the shader/ effect, from vertex to pixel shader, how to read textures and so on.