The statue was most likely made in 19th century. 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. The position of the arms of the statue in question shows that its hands probably held the crucifix, which is an attribute of the saint, instead of holding a book.
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