The original song was sung by the Italian singer Tony Renis in 1962; its many American covers mostly only partially translated the original refrain /dimmi quando quando quando/ into /tell me quando quando quando/. quando: when (There are quite many better Italian songs around, imho)

Quando = When “Tell me, quando, quando, quando?!” It seems to be an expression of strong curiosity to know “when”.

Fun fact: "Cuando" is Spanish for "when". It is pronounced the same way as "quando". :)

Quando è lieto, quando è triste.

it is not English.......I just know that it seems to mean "when" in Italian