It's usually secured to the frame or suspension components. You'll likely need to get under the car to find it. Look for a cylindrical canister with various hoses connected to it. It's often black plastic.
Important Note: The charcoal canister doesn't actually filter the gas *itself*, but rather it filters *vapor* from the gas tank to prevent emissions. If you're having fuel-related problems, it's unlikely the charcoal canister is the source. You should consult a repair manual or mechanic for diagnosis of fuel system issues.
