Certified GKH Gardening Expert
Since your tree is still considered fairly young and may have been started by seed, it could actually take up to 10 years or more for it to begin blooming. In addition, nitrogen-rich soils encourage trees to produce more vegetative growth and fewer flowers. Therefore, additional phosphorus and micro-nutrients may help stimulate root growth and flowering. To feed the roots, make holes around the drip line of the tree, 6 inches apart and 8 to 12 inches deep, and add super phosphate (0-20-0) and your recommended micro-nutrients according to the directions on the bags.
To propagate a magnolia, here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/trees/tgen/how-to-root-cuttings-from-various-shrubs-bushes-and-trees.htm