Generally, it's located in the engine bay, but accessing it might require removing some other parts. To find it accurately, you should:
1. Consult your owner's manual: This is the most reliable source for the specific location on your vehicle's year and model.
2. Search online: Search for "[Your Trailblazer Year] air filter replacement" on YouTube or a car repair website. Videos often show exactly where the filter housing is and how to access it.
Without knowing the year of your Trailblazer, I can't give you a precise location.