The word "knocking" refers to the sound made when someone hits a door or surface with their knuckles or a hard object to get attention or gain entry. Full definition
Press releases, posters, bookmarks, and such won't make a difference if you're not out knocking on doors and setting up your own promotional venues. (selfpublishingrelief.com)
At least, in five years of knocking on doors, it's never happened to me. (leftfutures.org)
There is no official do not knock on door list as opposed to a do not call list. (religion.blogs.cnn.com)