Here are a few rewrites of the title “Media mogul Barry Diller reminisces on his life and career in memoir ‘Who Knew'”:

Focusing on the personal reflection:

• Barry Diller looks back: Media titan shares his life story in memoir ‘Who Knew’.
• ‘Who Knew’: Barry Diller reflects on a remarkable life in media.
• A media empire revealed: Barry Diller’s memoir ‘Who Knew’ offers a personal journey.

Focusing on the career aspect:

• Barry Diller’s media journey: ‘Who Knew’ chronicles a legendary career.
• From mailroom to mogul: Barry Diller’s story unfolds in ‘Who Knew’.
• ‘Who Knew’ tells the story of Barry Diller’s rise to media power.

More concise options:

• Barry Diller’s memoir, ‘Who Knew,’ explores his life and career.
• ‘Who Knew’: Barry Diller’s reflections on a life in media.

More attention grabbing:

• “Who Knew”: Media Mogul Barry Diller spills the tea on his life and career.
• “Behind the Empire”: Barry Diller’s new memoir “Who Knew” tells all.

The best option depends on the specific angle you want to emphasize.