If you own the Blu-ray or 4K UHD disc:
While popular, this method carries significant risks:
Let’s be clear: Downloading copyrighted audio tracks from torrent sites without owning the source material is illegal. However, there are legitimate workflows to obtain the English audio track.
The Dark Knight is NOT public domain. However, sometimes hosts fan-edited audio commentary tracks or isolated score mixes that do not contain the full film dialogue. Search for "The Dark Knight isolated score" rather than the full track.