Otomo is not really correct unless the question is about the person who accompanies a teacher on a trip. O is an honorific. It does not mean great. Tomo is attendant. Friend is a different word.
Deshi or uchi deshi could be possible as in Matthew's post.
Thanks, Niall! I did confuse the examples. I was thinking of times when I would travel with Sensei Barrish to Canada for a private training, but then related that experience to what the uchi deshi commonly experience in terms of attending to the needs of the sensei, guests, and the dojo in general. I was just trying to comment on the idea of training the attention; which means I was a little off-topic too, sorry.