The Mona Lisa is a painting done by the human Leonardo da Vinci during the 15th century in Europe on Earth. Her enigmatic smile has engaged viewers for centuries, and in the 21st century the painting was on display at the Louvre Museum in Paris, France.
By the 24th century, Kivas Fajo was in possession of the Mona Lisa, and it was one of the centerpieces of his illegal collection. During his captivity, Data tried to mimic the Mona Lisa's famous smile. (TNG: "The Most Toys")
Since Fajo's collection was confiscated after his arrest, it can be assumed the Mona Lisa was eventually returned to Earth and likely put back on display at the Louvre.