They are all over herbivore island, if you are wanting to tame one it would be best to find an alone one because if one gets hit they all come for you and it is best to walk in a straight line in front of them and keep hitting them in the head with trank arrows until knocked out.
The Ankylosaurus will not attack you in the wild unless you attack first. When battling you can run away quite easily, just be aware, they have high health, so if you plan to kill one make sure you have enough stamina and resources to kill them.
Tame one, lvl up health, stam, speed and damage as high as possible then go destroy rock golems and gather rare resources. Best dino for it. Tamed 3 and destroyed a golem in 3 whacks of their tails. Happy Hunting.