Ken has HNM sight radius, in that if you can see him, he can see you and it's game over.
He has the natural 90 degrees area of sight in front of him, but he turns and moves around a lot.
His HP will drop, and he can be KO'd, so keep his HP high.
The only time that is really safe to cure him is while he's in battle.
The path is one set path. He does a loop on the left-hand side of the entrance of Dangruf and goes through a few regions. Curative jobs are required, unless you have an escort of your own to kill everything in the way ahead of time.
When he engages a monster the game remember his position that he was on along along his path.
When that monster dies, he will turn around, head to that spot in his path, then continute along his way.
You have 30 minutes to complete this quest. The reward is 1,500 gil.