The melody of Knock Three Times by Tony Orlano & Dawn runs 249 notes across 27 bars, 2:31 long in D at 100 beats per minute. The tab sits almost entirely in the first two frets, one note at a time — no chords to barre and no strumming pattern to keep up with. A piano backing track plays the chords and bass underneath, so the line you are learning sounds like the record even at half speed.
Prefer to strum and sing it instead? Knock Three Times chords and lyrics.