Many thanks to @keanulatino for tweeting the link!
Professor of Engineering and Technology, Mauricio Molina worked on the live sound capture for Knock, Knock and is also working on the sound during the post-production stage of the film.With regards to working with Keanu Reeves, he said:
I was much struck by his professionalism and how easily joined the team.
The article is in Spanish and translates well with the google translator. You can read the entire article and his other comments about the film here.