One of the Equus locations. Take the taming quest it'll show you where they are (not sure if this is still relevant but if anyone need this, it's here just in case) :
Demon Equus - ARK Official Community Wiki
Equus - ARK: Survival Evolved Wiki
Can't find a unicorn | Ark Survival Evolved Amino
Ark Mobile Equus Location | Ark Mobile Equus Spawn Locations - YouTube
How To Tame Equus in Ark Survival Evolved | The Nerd Stash