For the specific release you mentioned, you can typically find and download compatible subtitle files (often in .srt format) on popular repositories like OpenSubtitles or Subscene. Knock Knock (2015) - Plot - IMDb

: The girls hold Evan hostage, physically and psychologically torturing him. They deface his home and destroy his wife's valuable artwork as part of their "lesson."

: The next morning, Evan's guilt turns to terror when the girls refuse to leave. They reveal themselves to be dangerous sociopaths who play a "game" of targeting and punishing married men who succumb to temptation.

: The film concludes with a dark twist where the girls bury Evan up to his neck in the backyard. They record his "confession" and post it to his social media, ruining his life before departing to find their next victim. Finding Subtitles

: Evan allows them in to dry off and wait for an Uber. Despite his initial resistance, the women aggressively flirt with and eventually seduce him into a threesome.