George Kaplan, Combs' former personal assistant, was granted immunity to testify after initially telling the court that he would invoke his Fifth Amendment right against self-incrimination.

Prosecutors are aiming to fill in the picture of the mogul’s relationship with Casandra Ventura by questioning his former assistant and Ms. Ventura’s mother.

“I had a whole other job,” she said. “Basically a sex worker," she said, referring to her role in "Freak Offs" — the orchestrated, days-long, drug-fueled sex sessions Combs allegedly forced her to par...