Thor was laughing in Karl's mind that they thought just any human cleric would be compatible with his skill. Blue Dragons had lightning breath, of course their High Priestess would be compatible with Refreshing Lightning. Nature Priests might as well, since they were more attuned to animals than humans. But the average, run-of-the-mill cleric, guard or any other class? Highly unlikely.
Maybe a Druid might be able to use it, but Thor didn't know any Druids, he had only heard of them and seen a few.
"You seem to know something that the rest of us don't." The High Priestess informed Karl with a serious look.
"Blue Dragons have lightning breath." Karl replied simply.
The High Priestess facepalmed, and then sighed. "Of course they do. So, it's not a matter of just the class category, you have to have an affinity for Lightning. Alright, I will have to make copies later, and then teach them to some other Blue Dragon Clerics.