Talk to Mira with a stupid character and at least 7 Strength; Merk will point the Chosen One in her direction if spoken to. She will tell the player character to climb a rope over the city wall.
If it is nighttime when entering downtown, Jack will be in the police station. Wait until dawn and he will walk over to the power station and threaten to blow himself up, which is the best opportunity to waste him without annoying anyone; one can actually let him blow himself up with the same result. When he's dead, head over to the bazaar and talk to Mira to claim the reward.
For a normally non-stupid character, the best time to get this quest would be after talking Jack out of blowing himself up. Use Mentats if Intelligence is below 7, Psycho and/or Buffout to get the quest, then go kill Jack silently in his cell for the 2000 XP. IN must go back below 4 to collect the reward.
If one fought Lenny in the ring, Mira's dialogue will be different, thus the quest is unattainable.
If one already gotten the quest, Mira's reward can't be gained (whether 'stupid' or not).