Answer:
What triggered the riots at Ephesus that almost killed Paul's companion was Paul casting out demons and converting many pagan sorcerers who burnt their expensive magic texts.
Step-by-step explanation:
Because of this act of Paul, he makes enemies with Demetrius who is a silversmith that makes and sells images of Artemis.
Demetrius stirs a riot because of the loss in trade he suffered and Pauls companions Gaius and Aristarchus are almost killed.