I could find a "Nic. Milowitsch" at "castlegarden.org". He had 1873 emigrated. And I also have looked in an archive of North Rhine-Westphalia in the emigration data in the time. No Millowitsch emigrant was recorded there, however! It means: If he had actually emigrated of Cologne, then he had emigrated perhaps illegally. Or he had emigrated from another area of Germany ("Prussia").