Obi-Wan gets information about the dart at Dex's Diner in Star Wars: Episode II - Attack of the Clones.
After discovering that the assassin Zam Wesell used a poisonous dart, Obi-Wan takes it to Dexter Jettster, an old acquaintance who runs Dex's Diner on Coruscant. Dexter recognizes the weapon as a Kaminoan saberdart and explains that it comes from Kamino, a planet missing from the Jedi Archives.
That conversation gives Obi-Wan the clue he needs to continue his investigation. He asks the Jedi archivist Jocasta Nu about Kamino, but the planet does not appear in the Archives. Obi-Wan then consults a three-dimensional star map and eventually finds Kamino in the stormy region south of the Galactic plane.
Dex's Diner is more than a quick stop in the film: it connects Obi-Wan's street-level investigation to the larger mystery of the clone army. A common mix-up is naming Kamino as the location where he gets the information. Kamino is the answer revealed by Dexter; Dex's Diner is where Obi-Wan learns it.