Boars can use Charge, Growl, Cower, Bite and Dash. Only boars can use Charge.
You can find this information in a webarchive of the old Petopia here:
http://web.archive.org/web/200704081823 ... list.shtml(But Ignore the skills/pets added in 2.0 ).
To get the ability in your pet training book, you have to use it.
With longer cooldown abilities such as charge, this can take quite some time.
Use your pet to charge a mob, kill it, wait for charge to cool down, then try again.