Obtained: Speak with Oolong at the Kame House
Objective: Head to Kami’s Lookout
Speak with Oolong at the Kame House, then travel to Kami’s Lookout on the World Map. Once there, talk with Kami to ask him about Gohan’s tail. After the conversation, travel to the Giza Wasteland and track down Vegeta near the northern part of the area. Speak with him to trigger a cutscene leading to a fight. Defeat Vegeta to kind of gain the answers you seek. This will trigger another cutscene that completes the story.