Subjected to His Will is triggered after speaking to Cole after completing Here Lies the Abyss. This mission is mostly a story mission to determine the direction Cole's character goes, though it's mainly cosmetic and will not affect his abilities. In Skyhold, speak to Cole, then tell him that you will protect him due to his nature. Solas will come up with an idea to do so. This will unlock a new mission on the war map called “Obtain Amulet for Cole,” and it's located on the far east of the Ferelden side.