Lisbon — Isabel dos Santos, Africa’s richest woman, built her multibillion-dollar business empire via a series of questionable deals involving Angolan state assets during her father’s 38-year rule of the resource-rich nation, according to a report by the International Consortium of Investigative Journalists (ICIJ).

Dos Santos got access to lucrative deals involving state-owned oil company Sonangol as well as diamonds, land and telecommunications. Funds were diverted to offshore bank accounts linked to her and her husband, Sindika Dokolo, it said. The trove of e-mails, charts, contracts and accounts were mostly obtained by the Platform to Protect Whistle-blowers in Africa and shared with the ICIJ...