When is Saint Nicholas' Day?

Answer 1

We celebrate the day of his death December 6th of every year as St. Nicholas day.

St. Nicholas, the bishop of Myra, and Santa Claus are not the same although many people confuse them with each other.

The Dutch Protestants carried a popularized version of the saint's life to New Amsterdam, portraying Nicholas as nothing more than a Nordic magician and wonder-worker. Our present-day conception of Santa Claus has grown from this version. Catholics should think of Nicholas as a saint, a confessor of the faith and the bishop of Myra - not merely as a jolly man from the North Pole who brings happiness to small children. Many countries and locations honor St. Nicholas as patron: Greece, Russia, the Kingdom of Naples, Sicily, Lorraine, and many cities in Italy, Germany, Austria, and Belgium.
"Saint Nicholas (Greek: Άγιος Νικόλαος, Aghios["holy"] Nicolaos ["victory of the people"]) (270-6 December 343),[3][4] also called Nikolaos of Myra, was a saint and Greek[5] Bishop of Myra (Demre, in Lycia, part of modern-day Turkey). Because of the many miracles attributed to his intercession, he is also known as Nikolaos the Wonderworker(Greek: Νικόλαος ο Θαυματουργός, Nikolaos o Thaumaturgos). He had a reputation for secret gift-giving, such as putting coins in the shoes of those who left them out for him, and thus became the model for Santa Claus, whose modern name comes from the Dutch Sinterklaas. His reputation evolved among the faithful, as is common for early Christian saints.[6] In 1087, his relics were furtively translated to Bari, in southeastern Italy; for this reason, he is also known as Nikolaos of Bari. His feastday is December 6."

Source: Wikipedia.