The house on Wareham Place has become another curiosity in the vast orbit of properties connected to Mr. Trump, even though he last lived in the five-bedroom home, built by his father, Fred C. Trump, when he was 4. The house’s intrigue lies not just in the price it fetched in an auction by Paramount Realty USA — $2.14 million, more than double the price of comparable houses in the area — but also in the mystery surrounding the buyer. She remains unknown, shrouded behind the limited liability company.

A thin trail of documents associated with the sale led first to a second-story office on Main Street in Flushing, Queens, of Michael X. Tang, a lawyer who represents Trump Birth House. In the cramped and bustling office, which, according to its website, specializes in facilitating Chinese purchases of American real estate, a woman at a desk welcomed visitors.

“Oh, about the Trump house,” she said. She continued: Mr. Tang declined to comment.

Documents show that Mr. Tang was also the lawyer for a seemingly unrelated transaction on a palatial home in Old Westbury, N.Y., which sold for more than $3.6 million in 2014 to a person named Jiying Wei. The redbrick mansion, tucked at the end of a cul-de-sac and abutted by a private tennis court, is a far cry from the modest butter-colored childhood home of Mr. Trump. But, according to a person with knowledge of the sale, the mansion’s owner is a relative of the woman from China who bought the Trump family home.

Standing in the collonaded entryway of her home a few doors down in Old Westbury, a neighbor, who declined to give her name for privacy reasons, deepened the mystery: The only person who lives in the mansion, she said, is the family’s son, a local college student; the rest of the family lives in China.

The trail dead-ended at the cul-de-sac: The house was empty and the owner could not be reached.

“I did have some expectation that the purchaser would be a huge Trump supporter from within America,” Misha Haghani, principal of Paramount Realty USA, said of the Jamaica Estates home. He declined to reveal the identity of the buyer. “But it is entirely possible that the purchaser is a huge Trump supporter from outside of America,” he said.