To enslave someone target them with and then hit , release it before they are dead. I would recommend not upgrading your target spell more than once, perhaps twice, as it’s easy to kill them by mistake. As with “Walking Apocalypse” some areas are only accessible later in the game. Breaking down doors to release townspeople has no effect on your domination % and needs to be done to dominate all 100 villagers.
In Nordberg there is an area which can only be accessed when you have green minions to destroy a barrier and another that requires blue minions to move a raft. In Everlight an audience later in the game will give you a sidequest to open the final area there which contains the last 20 townspeople. You have to be very careful here not to kill any villagers as they appear red and your minions will attack them, keep most of your horde well back. Two villagers appear after you destroy the second group of stilted huts. (the first chuck poison bombs, the second ground has one poison bomb and one exploding bomb, the two appear after you destroy the exploding bomb hut) these two will run towards your minions so make sure to keep most of your horde well back and to enslave them quickly. For the next section take only the green spider riders and run them up the wall to dislocate the bombers, if you don’t do this they will likely kill some villagers. Once this is done the quest ends and the remaining townspeople return to being green. It’s best to save before this quest as it can take several attempts.
If you cannot find a villager try gating out of the map and then back to it, this will spawn all townspeople again and replace the doors on houses that still contain any.