The outer bottom piece that has the chrome trim and the rubber seal against the window.
THose are the following part numbers:
92277518 Right Rear Door
92277517 Left Rear Door
92277514 Right Front Door
92277513 Left Front Door
But unless yours are rotten with holes on them no use replacing them. Even new they are going to let water into the door. Protecting the latch electrical connector is a good idea. The approach I have taken is to concede that water is going to come in and use a liner inside the door to keep the water off the vapor barrier and to direct all the water to the inside of the bottom of the door. Link to the idea on my front door:
PPV Water Leaking Through Door Panels
Then of course just make sure the holes at the bottom of the door are clear of debris and the rubber seal covering them is letting that water out. Sometimes the rubber can get so stiff it actually blocks the water from exiting.
2011 Caprice PPV