So how to get the sense logan ride the fat bandit ?
When the bandit attack happens to the human town on day 20 or higher after doing the story quest where you cure the shopkeeper of his sickness and visit him the day after giving him that, when you talk to logan about the bandit attack, choose to Encourage him to go to camp, this will start him going down the path where he does that at night to him.
If you mean about this, try finding Jester at night, talking to him about the topics, doing the 2 quests from him, getting the scene that trigger with Scar at night, then the one in the bandit camp when choosing to sneak in at night, i think submitting to the 2 bandits guarding the place might eventually lead to Logan being found, he will have the 3 purple ? marks if you trigger the scene with him in the bandit camp, you can choose to offer yourself in his place after that to free him.