In this video artist plays note using his little finger just before 2.9s which sounds like muted play. What is this technique is called. Please provide useful tutorial to learn this technique.
It's called a string harmonic https://en.wikipedia.org/wiki/String_harmonic
String harmonics are "high pitched tones, like a whistle's, are produced when the musician lightly touches certain points on a string."
To play the octave harmonic, the player lightly touches the string at exactly halfway between the ends of the string's vibrating length, which is where the octave fret is. And while touching the string at that point with the fretting hand (left hand), the player picks or fingers the string with the picking hand (right hand). It sounds like a flute or a whistle. The octave fret, i.e. 12th fret, is the easiest place to get a harmonic. Other places are e.g. 5th and 7th fret.