I recently own B6 3.0 quattro. I have some tough time to locate the cabin air filter.
Does anyone know where the cabin air filter is located and how to change it?

 

Check under the cover at the base of the windshield in the engine compartment, on the passenger side. Pull back the weather stripping to loosen the cover and it should be in a plastic housing. Open the top of it and it's right there.