The painting was mentioned in the visitation records from 1765, thus it had been created for the finial of the high altar before that year. It was probably made by Kazimierz Mołodziński. Saint John of Nepomuk was a canon of the Collegiate Church of St. Giles in Prague, which is why he is portrayed in attire corresponding to this position. He is usually shown during his adoration of crucifix, which is in his hand.
Paulina Kluz, "St. John of Nepomuk", [in:] "The Sacred Lesser Poland Heritage", 2024, source: https://sdm.upjp2.edu.pl/en/works/st-john-of-nepomuk-5