Showing you where the location of Vault 114 is and how to get there.
The access point is at "Park Street Station" close to Diamond City.
The Quest "Unlikely Valentine" from Diamond City is getting you to Vault 114.
The Speech Bobble Head is on the Desk of the Overseer's Office. Following the Quest will lead you to this office.
Finish the Quests "Short Stories" and "Here Kitty, Kitty" to get the "Hole in the Wall" Quest. Right at the end of the quest you'll find the Medicine Bobblehead. Stimpaks permanently heal 10% more damage.
Don't forget to pick up the reward for that Quest: SHORT SYRINGER RIFLE