I don't recall ever having seen the Charging skill show up in my village for my paladin - and I can't use the Riding skill until I have Charging. Anyone else come across this? How do I access the Charging skill?
I am unsure what your paladin's level is, but at each level, your paladin will get a random book. To unlock Riding, which is tier 2 your paladin will need to be both level 8 and have at least 1 point in the charging skill. To get the charging skill, you can level up to get more books or reroll one of the other tier 1 books (Motivation or Swordplay) to try to get it.
HERE is an article on the Paladin's skill set. It has more information regarding the different skills as well as how they work.