| Claxon |
Yeah, the weapon needs to have the trait or you run into action economy issue or you need a feat that allows you to do it.
Chances are you're already playing a martial character, in which case hopefully you're a fighter and you already have Knockdown as an available feat choice.
If not you can multiclass into mauler, to pickup knockdown and improved knockdown. But knockdown with improved knockdown is VERY good. It is really worth taking if you are a fighter, and can be worth it even if you need to spend the feat to multiclass but would gain nothing of use from mauler.