Tokkey is a researcher of music who lives in a secret grotto in Talus Peaks, an area located near Symmetry City in the Present. His house can only be accessed by discovering the hidden path under Talus Lake, which Link will have to swim around a bit to find. Tokkey's main goal lately has been to create a tune that would allow one to travel forward through time. However, he seems to have reached a roadblock along the way after encountering a riddle which states Echoes produce waves.... Tokkey will only be able to continue his research in creating this tune if he is able to figure out the riddle.
The answer to Tokkey's riddle is the Tune of Echoes, which Link was taught early in his adventure after obtaining the Harp of Ages. After playing the Tune of Echoes for Tokkey, he will then figure out the riddle and be able to create the Tune of Currents, which he will then teach to Link. The Tune of Currents allows Link to travel from the Past to the Present in any location as opposed to having to stand on the Time Portals while playing the Tune of Echoes.