Puzzles/Logic puzzles/Three Knights/Solution
The small knight is the Knight of Life. The fat knight is the Knight of the Dungeon. The tall knight is the Knight of Death.
The tall knight is not the Knight of the Dungeon, since if he were neither of the other knights could be the Knight of Life. Since he lied, he is not the Knight of Life. Therefore, the tall knight is the Knight of Death. The small knight must then be the Knight of Life, leaving the fat knight as the Knight of the Dungeon.
Provided the fat knight tells the truth he can not be the Knight of Life as he is pointing out the tall knight as Knight of Life. The answer of the tall knight contradicts the answer of the fat knight. Therefore, the fat knight was lying. The tall knight can not be the Knight of Life, because he would have said so when directly asked, who he is. We can conclude that the small knight is the Knight of Life and he is pointing out the tall Knight as Knight of Death as he is always telling the truth. The last job positon left for the fat knight is the Knight of Dungeon.
The convict can be happy that the tall knight did not answer: 'Yes, I am the Knight of Life'. In this context, it would have been possible and would have left our convict very unfortunate, because his chance to find the Knight of Life would have been reduced by 50%
A better tactic would be to ask each Knight: "If I asked you who the Knight of Life was, whom might you identify?" The Knight of Life would correctly identify himself. If asked "Who is the Knight of Life?" the Knight of Death would incorrectly identify either himself or the Knight of the Dungeon. Hence, when asked how he might respond, he would lie again, and state that he would have identified the correct Knight of Life (double negative). The Knight of the Dungeon is the unknown quantity, but when at least two Knights agree on someone, that is the correct identification.
Unfortunately not foolproof, as if he would have identified the Knight of the Dungeon for his first lie, he could then pick to instead identify the Knight of Death for his second lie.