Knock on/knock off is enabled by default. Slim does not have the ability to turn either off and never has. I know gmillz was working on adding it to the settings at one time, but I think he's moved on to more important projects for slim.
Please everybody stop posting about issues with rotation and autobrightness, because you are not using the correct modem. This has been a known issue on the g2 for months, not just slim.
Also, both of these issues are addressed in big bold letters at the top of the OP.