Pershing was the Commander (or Commanding General) of ALL the AEF Forces of WWI.
From Wikipedia..." Following America's entrance into the war, Wilson, after a short interview, named Pershing to command, a post which he retained until 1918. Pershing, who was a major general, was promoted to full general ... in the National Army, and was made responsible for the organization, training, and supply of a combined professional and draft Army and National Guard force that eventually grew from 27,000 inexperienced men to two Armies (a third was forming as the war ended) totaling over two million soldiers."
The 109th Eng was in the 34th Divison which was made up National Guard Units that were "federalized" from the states of IA, NE, MN,and SD. Here is a website to see the Shoulder/Sleeve Insignia as well as other details.