He was apprenticed to Franz Renn, an Imst woodcarver, after which he studied ancient German wood-carving at Munich under J. Otto Entres.
After completing his formal studies Knabl toured extensively through Middle Europe and became intimately acquainted with the finest examples of ecclesiastical sculpture.
That work depicts the Virgin Mary in larger-than-life size at the center of the high altar, surrounded by 6 worshipping angels.
His work at the Mayer Institute, where he not only produced numerous drawings and sketches, but also trained capable scholars, furthered the diffusion of a cultivated taste in religious art.
Most of his works are in Bavaria (Munich, Haidhausen, Passau, Eichstadt, Velden), but there are also some in Stuttgart, Mergentheim, and in other places.