Grong Grong is not a real geographic location. It exists solely as a fictional setting in the 1996 live-action/animated film Space Jam, starring Michael Jordan and the Looney Tunes characters.
In the movie's narrative, Grong Grong is depicted as the home planet of the Nerdlucks (later known as the Monstars)—small, weak alien creatures who work for the evil intergalactic amusement park owner, Mr. Swackhammer. The Nerdlucks travel from Grong Grong to Earth to kidnap the Looney Tunes characters for Moron Mountain, Swackhammer's failing theme park.
The name "Grong Grong" appears to be a playful, nonsensical construction typical of Looney Tunes humor. Interestingly, there is a real Grong Grong, New South Wales—a small village in Australia's Riverina region—but this is purely coincidental and unrelated to the film.
Space Jam blends basketball, animation, and sci-fi parody. The fictional planet serves as a narrative device to explain the aliens' origin and motivation. The film's success spawned a 2021 sequel, Space Jam: A New Legacy, though Grong Grong is not prominently featured in the follow-up.
Bottom line: If you're looking for Grong Grong on a map, you won't find it—unless you're mapping the Australian village. In the Space Jam universe, it's the distant world where the Monstars began their journey to challenge Earth's greatest basketball player and beloved cartoon icons.