The Kazooie Switch is a gray-white colored switch with Kazooie's face on it. It is only seen in Banjo Tooie. You can only activate it by stepping on it as Kazooie. You will need to use a Split-Up Pad to play as Kazooie by herself. You can press A to switch to control of Banjo after stepping on a Kazooie Switch. These switches can be found in almost every world, and are usually next to a Banjo Switch.
You will need to step on a Banjo Switch and a Kazooie Switch in the 9th and final world, Cauldron Keep. Stepping on both switches correctly will open the gate so you can progress to the 3rd Klungo fight.