Wiki - Pet Powerscrolls
Normal Powerscrolls may be used on a pet, but this method requires the skills to be purchased through advancing with the Pet Training System. For example, training wrestling up to 120 through the training menu will require you to have a 120 wrestling powerscroll in your pack. This method will also cost you points in the training menu.
The second method is the use of Pet Powerscrolls. These are less common, being only available as Taming BOD Rewards, but will allow a pet to naturally advance skills that they currently have and use past the 100 cap without having to spend points through training.
Please note that Pet Powerscrolls will not give a pet a skill that they do not have. They only allow skills a pet actively uses to train past the cap. It is possible to waste a scroll on a pet that does not actively use the skill, user beware. Skills may be added through the training system only.