If you're interested in finding John Schopf, look at the 1910 Read, Clayton Co., IA Census. There is a John Schapp living with the Stoops family. He was born abt. 1846, Germany and widowed and immigrated in 1870. Since he was 64 at the time, he probably died in this area.
You are VERY lucky you knew about Dorathea's multiple marriages because I sure couldn't figure it out from the Censuses. Best of luck in your research!