The windshield washer fluid reservoir on a 2004 Chevrolet Trailblazer is typically located
under the hood, on the passenger side. It's usually a fairly large, plastic reservoir with a cap that's clearly marked "Washer Fluid" or with a similar symbol. Look for a plastic bottle-shaped container.
If you can't find it easily, check your owner's manual. It should have a diagram showing the location of all fluid reservoirs.
