The spark plugs on a 2002 Chevy Trailblazer are located on the top of the engine, under the plastic engine cover. To access them, you'll need to remove the engine cover. They're arranged in a V-shape, following the configuration of the engine's cylinders. You'll find them near the valve covers.
However, the exact location within that general area varies slightly depending on whether your Trailblazer has the inline 6-cylinder (I6) engine or the 4.2L V6 engine. A repair manual specific to your vehicle's engine is highly recommended for precise location and removal instructions.
