Republican presidential nominee Donald Trump’s son Eric Trump questioned Friday how Democratic nominee Hillary Clinton and former President Bill Clinton became enormously wealthy running a charity, which has become the focus of the campaign’s allegation of pay-to-play corruption while she was secretary of state.

“The question I always ask is, what product were they selling? If we make a buck, we sold a bottle of wine or an apartment, or we sold a hotel room. What product were they selling to make $150 million,” Mr. Trump said on Fox News’ “Fox & Friends.”

Host Ainsley Earhardt suggested: “Favors? The government?”

“Of course,” responded Mr. Trump, who works on the campaign for his billionaire businessman father.

“This is the leadership we have in this country. Somebody sets up a foundation. They pocket hundreds of millions of dollars. They say they come out of the White House ‘dead broke.’ Now they are worth $150 million,” he said.

Mrs. Clinton famously claimed that they were “dead broke” when they left the White House in 2001.

Mr. Trump was citing a high estimation of the Clinton’s wealth. Other estimates peg their net worth at a combined $111 million, with Mr. Clinton worth approximately $80 million and Mrs. Clinton worth just over $30 million.

“It’s just so so sad,” Mr. Trump said. “People in this country work so hard and sometimes they are not able to achieve because of the policies that these politicians put in place and look what they do.”

The Clinton Foundation has become a focus of questions about potential conflicts of interest while Mrs. Clinton served as secretary of state. The charity accepted donations from foreign entities with interests in State Department policy.

The lines between Mrs. Clinton’s agency staff and the work of the Clinton Foundation also were sometimes blurred.

Some of Clintons’ wealth came from generous speaking fees paid to Mr. Clinton by foreign entities while his wife was secretary of state. His usual fee of $150,000 climbed higher while his wife was in office, including a $500,000 fee paid by a Russian investment bank with links to the Kremlin and a $550,000 fee paid by a Chinese business group for a speech in Shanghai.

After she left the State Department in 2013, Mrs. Clinton started collecting $200,000 speaking fees, mostly from trade groups and Wall Street banks, according to an analysis by the Associated Press.

Financial disclosures showed that the post-State Department speeches earned Mrs. Clinton nearly $22 million.

As secretary of state, she earned $186,600 a year. In her prior role as a U.S. senator from New York, her annual salary started as $145,100 in 2001 and rose to $169,300 in her final year in 2008.