Here's the only reference I can find to that assembly discourse. Beginning in September of 1970, it may have been given for the following six months.
A new circuit assembly program is scheduled to begin in September. We believe you will find it most informative and upbuilding. The public talk will be “Who Will Conquer the World in the 1970’s?” Our Kingdom Ministry, 7/70 p. 3 Announcements
As to Knorr and his little buddy, they were both still going strong in early 1971 as noted by the following:
In this country of about four million people, 80 percent of whom are Moslem, 178 of Jehovah’s witnesses carry on their preaching activity. The assembly was not advertised, but was in the nature of a private gathering. The peak attendance was 325. Both the president of the Watch Tower Bible and Tract Society, N. H. Knorr, and the vice-president, F. W. Franz, appeared several times on the program, speaking through interpreters. The Watchtower, 1971 2/15 p. 123 Is Unity Possible Among All Ethnic Groups? Fats