DETROIT — President-elect Donald J. Trump is not attending the country’s premier auto show here. But his vow to impose tariffs on imports from Mexico has changed the focus of the show from what new vehicles are on display to where they are made.

More than anything, said Sergio Marchionne, the chief executive of Fiat Chrysler, the industry needed to know what was going to happen with the North American Free Trade Agreement, which allows for a free flow of trade between the United States and Mexico.

“We need a clear indication of how the U.S. administration plans to deal with Nafta,” Mr. Marchionne said at the auto show. “We’re just waiting for clarity.”

Mr. Trump has made the auto industry a frequent target, attacking automakers for selling Mexican-made vehicles in the United States. In response, some automakers have somewhat changed their strategy.