IRBIL, Iraq — For three years, he worked closely with U.S. forces in Iraq. Now Ammar Younes sits in his frigid tent in a camp in Iraq’s Kurdish region, using a scalpel to gouge pieces of shrapnel out of his mangled legs as his young children look on. A trainer in the Iraqi army, the 34-year-old was wounded when Islamic State extremists placed a bomb under his car in Mosul in June, just a week before the northern city fell to the militants. He was forced to flee his hospital bed, still wearing his medical gown, when the city was...