Where to find the Appian Play book?

You mean this?  It looks to me as if all it requires is a valid Community login (I was able to open it fine, though when I open it in an incognito window I notice it asks you to log in).  I don't have any inside information as to whether there is some additional privelege needed to access it, on top of a basic community account - if so, hopefully an Appian employee can chime in here.

I'd like to know more about this course

You can find the Appian Playbook here

community.appian.com/.../the-appian-playbook

Hi, the Appian Play book is available at this link : https://community.appian.com/w/the-appian-playbook

Manually Enter this URL in the browser if clicking on the link doesn't work: "community.appian.com/w/the-appian-playbook"

For documentations check this,

docs.appian.com/.../