Knock Sensor 1 -G61-, REMOVING AND INSTALLING: Notes
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2020 Audi A4 allroad, 2020 Audi A4 Quattro, 2019 Audi A4 allroad, 2019 Audi A4 Quattro, and 2018 Audi A4 allroad. However, it is still accessible from the selected car via links, so may be relevant.
Component location: under the intake manifold behind the Engine Temperature Control Actuator -N493-.