Sonja, I'm not sure if we have any connection or not, but I'm also researching the KNAAK/KNACK line.
My great-grandfather was Gustav August KNACK, born 22 Nov 1866 in East Prussia (that's all I know). He had a brother, William. William married Wilhelmine (don't know maiden name) and they had Ida (b. 10 April 1891) born in Goldap, East Prussia. Ida had a sister, Elvera.