I have blogged on both these subjects. For reference, first my bibliography:
First Universal Races Congress, London, July 26-29, 1911: Selected Bibliography
The conference proceedings can be accessed online. I see no contribution by Scarborough in it, though he did participate:
Papers on Inter-Racial Problems, Communicated to the First Universal Races Congress, Held at the University of London, July 26-29, 1911; edited by Gustav Spiller. London: P. S. King & Son; Boston: The World’s Peace Foundation, 1911. xlvi, 485 pp.
In his autobiography Scarborough gives an account of his participation in the First (and last) Universal Races Congress in London in July, 1911:
Autobiography of William Sanders Scarborough: An American Journey from Slavery to Scholarship, edited and with an introduction by Michele Valerie Ronnick, foreword by Henry Louis Gates, Jr. Detroit: Wayne State University Press, 2005. (Contents.) See chapter 19: Second Trip to Europe -- Delegate to the First Universal Races Congress -- [A] Rhine Trip; pp. 214-224. There is a prefatory remark on p. 213. The relevant information can be found on pp. 214-219, and in the final paragraph of p. 224. See also footnotes, pp. 378-380.
Following the commencement, I made preparations for my second trip to England as a delegate to the First Universal Races Congress to be held at the University of London in July where I was to present a paper. [p. 213]Scarborough mentions his correspondence with W.E.B. Du Bois, who organized a Negro American delegation. Scarborough describes his sea journey with his wife to England, and his encounters on board, e.g. with Albert Bigelow Paine, designated biographer of Mark Twain, a friend of the Negro cause. Scarborough sketches the proceedings of the Congress, participants, and papers, and a press report.
But the keynote of this wonderful assembly was the unity of the human race and the brotherhood of man. Whatever the subject discussed the brotherhood of man was never lost sight of. It was advocated and emphasized by the followers of every sect and creed and all from the same platform. With this as a basis of equality of rights and opportunity, fair play in the race of life was urged by both Jew and Gentile. Scarborough continues to outline the other functions and encounters connected with the Congress. After visiting Cambridge University, he and the wife are off to Paris. He returns to the theme of the Congress at the end of the chapter.
In the end we were at home again to receive a glad welcome and to report the Congress to school and friends, back from the great Races Congress, hoping that the men and women who claim to be such firm believers in the brotherhood of man will practice what they preach, and will help hasten the day when there will be no race problem. The future will show whether there has been any real substantial gain by such a concerted movement. Ouch!