In 2293, the location of Kling in the Milky Way Galaxy was labeled in a star chart that was in Captain James T. Kirk's quarters aboard the USS Enterprise-A. (Star Trek VI: The Undiscovered Country, okudagram)
Background information Edit
According to the Star Trek Encyclopedia (4th ed., vol. 1, p. 426), at the time "Heart of Glory" was written, Kling was intended to be the name of the Klingon Homeworld. Once the episode was filmed though, it was realized that the name sounded pretty silly, so later scripts simply referred to "the Homeworld", and the authors of this reference work now asumed that Kling was a city or district on the homeworld. The next time the Homeworld was given a name was in Star Trek VI: The Undiscovered Country, when it was called "Kronos". The spelling "Qo'noS" was subsequently devised by Marc Okrand, to conform with the rules of Klingon orthography. In dialogue deleted from "Heart of Glory", Worf said, "Could we speak English, sir? I am not comfortable in Kling." with the implication being that Kling was the official name for the Klingon Language, as well. 
According to The Worlds of the Federation (p. 45), Kling or Klinzhai were alternative names for the Klingon Homeworld. Also, according to Star Trek: Star Charts (p. 55), Kling was an alternate name for Qo'noS.
The short story A Warrior's Path in New Worlds, New Civilizations, references Kling as a city on Qo'noS.