planted 2 pecan trees 6 years ago. One has pecans & the other none. Can anything be done to promote pecans?

Question

Both trees look healthy. The tree with no pecans looks even healthier than the tree with pecans.

Answer 1

Here are some possible reasons pecans don't produce and also cultural requirements, particulary irrigation and fertilization that should help. Also, you should have a Type 1 and a Type 2 variety of pecan tree to aid in cross-pollination. You may not have both. Here is more information:
https://ucanr.edu/sites/Shasta_College_Master_Gardener/files/253043.pdf
https://www.gardeningknowhow.com/edible/nut-trees/pecan/growing-pecan-trees.htm