Knaphus was a Mormon convert, who produced many sculptures and bas-reliefs for LDS temples, as well as busts of famous Utahns, decorations for office buildings, mortuary and chapel friezes. His best known work is the Handcart Monument, one of the most recognized symbols of Mormonism. The heroic size version stands in Temple Square in Salt Lake City.

Perhaps his best-loved secular monument is the 1937 School Children’s Monument near the west entrance to the Salt Lake City and County Building. It features a granite base holding a scroll depicting the United States constitution. On either side of the base, facing each other, are life-size statues of a boy and girl looking up at the United States flag atop the seventy-foot flag pole set in the base. The statue honors school children, whose nickels and dimes paid for it.