Ghul Matrons are like elite Ghuls. They are kinda hard to find, but there are a few ways to find one. First of all it needs to be night time or else they probably wont spawn. You can advance time to make it night at one of the forge towers. When its night time you will need to go to an area of the map thats away from “civilisation”. Look out for the small claws on the map. Once you spot one you have found a Ghul nest.
Sometimes you might find a Ghul matron, but usually you need to draw one out. To do this you will need to kill a few normal ghuls. Once they start retreating, leave them alone and they will burrow into the ground. After a few seconds more will come out of the ground. Keep doing the same thing and eventually one will spawn.
Heres a video that shows you how to find a Ghul Matron.