I've realized that if my Star Wars: The Old Republic companions had as many abilities as I did, it would needlessly complicate the gameplay. But, for some of my companions, I can't tell if their abilities have changed at all throughout the course of the game. I don't have any character above level 15, so I may have just not seen it yet.
Like the title says, do I have to train my companions like I have to do to gain my abilities, or do I not have to worry about them as they'll gain those abilities on their own.
Best Answer
As of Patch 4.0, Companions come with all five of their abilities and do not gain any as you level. Previous answer below.
Companions gain abilities by themselves, they don't have trainers. I'm not exactly sure when however. They usually default to disabled, so as you level make sure to check and see if they have new abilities to enable. They don't get more than 10 so you don't have to manage their quickbar (and can't, last time I checked).