How to teach an NPC a word of power?

Solution 1:

NPCs can be taught words of power by using the console command AddShout. TeachWord takes the player only, but AddShout is available for any selected entity.

One word of warning, tho':

NPCs will always use the maximum power level of any shout they know and are using, and if you teach e.g. Fire Breath to a follower, you are likely to get caught in the crossfire, if you'll pardon the pun.

While NPCs will recognize and use shouts given to them by use of AddShout, they will pay no heed to wether or not you are in the way, so if you give a shout to a follower, be prepared to die. A lot.