Rogge and Göring
In 1946, O. John Rogge was sent to Germany by the U.S. Department of Justice to investigate Nazi activities and, particularly, Nazi attempts to influence American politics and business before the war. During roughly 11 weeks of investigation, Rogge interviewed 66 people, including Hermann Göring and Joachim von Ribbentrop, and examined thousands of German Foreign Office documents. (Wikipedia)
Rogge's questioning of Göring produced information about an alleged German plan to invest large amounts of money in American industry. Contemporary reporting said Göring admitted that such a plan existed and that it had a dual purpose: expanding German influence in the United States and providing Göring with financial security. Oil investments were reportedly among the intended targets. (TIME)
Rogge wasn't primarily questioning Göring as part of Göring's Nuremberg criminal trial**. Rogge was conducting a separate Justice Department investigation while the major Nazi defendants were being held at Nuremberg.
What happened afterward
Rogge compiled his findings into a major report for Attorney General Tom Clark in 1946. The report dealt with what Rogge called Nazi penetration of the United States, including connections involving American political figures, organizations, and businessmen.
The report became controversial because it implicated prominent Americans. Parts of Rogge's findings reached the press, and Rogge subsequently left the Justice Department. His research was eventually published in expanded form as The Official German Report in 1961. (Wikipedia)
So, in simple terms:
Göring → was a major Nazi defendant at Nuremberg → Rogge interviewed Göring there → Göring provided information about Nazi financial/political activities involving the United States → Rogge incorporated that material into his investigation.
One caution:
Some later books and internet accounts make much stronger claims about what Göring supposedly revealed to Rogge. The contemporary evidence supports the American investment/influence investigation, but individual allegations should be checked against the original Rogge report and contemporary records rather than accepted wholesale.