Watch the Tap Harmonics online guitar lesson by Dmitry Lisenko from Percussive Acoustic Bass (Foundry)
Use your index or middle finger on your right hand to hit above the 12th fret. It's the same tapping technique, but now we're trying to get a harmonic sound instead of the note.
There are also artificial tap harmonics. You have to take a note with your left hand and tap 12 frets further, this way you can play the harmonic octave of the same note. It works for every note, and we can play some melodies with them.