Kamala teaching Picard how to play the instrument.
The Kriosian musical instrument is a large instrument from planet Krios that is similar in appearace to an Earth xylophone.
A Kriosian instrument of this kind was part of the holographic recreation of the Temple of Akadar that was to be the setting of the marriage between Alrik of Valt and Kamala of Krios.
It was part of the wedding ceremony to play the instrument according to a certain discipline, called Torze-qua. As Ambassador Briam was unable to attend the ceremony, Kamala taught Captain Jean Luc Picard how to play the instrument. (TNG: "The Perfect Mate")