Kenning isn't generally worth it
Consider the angle that your players aren't using Kenning because, well, Kenning isn't worth the cost; you spend an entire Willpower and the most your character gets is, "Yes, there is something supernatural within sensory range of me," without even the courtesy of learning distance, direction, or relative strength. The complete lack of useful information even if you do use it at an appropriate time (and then succeed on your roll) means that even if Kenning could be theoretically used in a situation you're better off not using it and instead trying to detect the supernatural/your enemies/weird things in some other fashion - like Contracts of Fang and Talon, Contracts of Communion, a bog-standard Perception check, a Token, Contracts of Spell-Bound Autumn, or more (honestly, the list of things just grows longer and longer with every supplement).
If you want them to be able to pick up on the presence of the supernatural in the area then I would suggest looking into the expanded Clarity rules in Rites of Spring, or finding other ways to drop hints. Perhaps someone using Contracts of Fang and Talon can pick up on an unusual scent (old blood on a vampire's ghoul servant, for example), or they notice odd traits with a Perception roll.
If you want a general ability to detect the supernatural, Contracts of Spell-Bound Autumn (Lords of Summer) has such a power at the first dot, making it a "teaser" Court clause that can be taught freely to anyone even without Court Goodwill or Mantle (see Changeling: the Lost's description of Court contracts) and it serves well for the purpose; not only is it cheaper than Kenning in terms of costs, but it works better.