Telltales And Related.

[Chosen One]

When you take a Telltale and related types of quests, give SOME idea of where the fucker is. If I can’t find him, I can’t kill him and I waste a half-hour searching for someone that doesn’t exist. 

[Programmer]

Every Telltale's location spawns on worldmap and is marked as yellow circle. It should be visible no matter where you're but I'm not sure if it works when you didn't visit WM's zone and square is black. Anyway, it isn't hard to find Telltales or most of quest locations but I can agree with you that more details might be provided in dialogs or somewhere else.

[Chosen One]

I searched every grid from Reno to San Fran to Shady Sands. No yellow circle.

I even stuck my head into V-13, just to see if he was hiding there.
Oh, and I’m not sure if it was a telltale; I got the job from a guy in combat armor in Junktown. (Oops?)