The phrase “who was on” is incomplete as a query and could refer to several different contexts. Here are a few common possibilities and brief clarifications to help target the request:

• If you mean a film, TV show, or historical event: specify the show, movie, or event, plus what you want to know (cast, participants, locations, dates, significance).
• If you’re asking about who was on a particular team, panel, list, or roster (e.g., “Who was on the US Olympic team in 1996?” or “Who was on the board of X charity?”): provide the organization and year or period.
• If you’re asking about a phrase like “Who’s on First?” (the Abbott and Costello routine): clarify you’re interested in the classic comedy sketch and its characters.

If you share a bit more context—topic, timeframe, and what exactly you want (names, roles, dates, or descriptions)—the answer can be precise and concise.