Many thanks to Dras ! for sharing a video on youtube and to @keanulatino for tweeting the link. He was a cleaning person and knew they were shooting. He took photos of the set. The ones with Keanu are at the following minute marks: 5:42, 6:07, 6:16 and 6:19.
Update: ana_d_armas has shared a photo that she took with Keanu on the first day of rehearsals on the Knock Knock set on websta.