I was able to confirm, through my friend in Vienna and the Jewish Genealogy Portal Facebook Group, that Klara Moretzki Kobak is indeed buried in Vienna. She never lived or visited the United States (she does not appear in any ship passenger registries or in US census records).
So, it appears that Leon Gideon Kobak (who seemed to prefer to be called “Leo”) did indeed travel to the US in 1898. But he did not stay (again, he never appears in any US census records). He traveled from Havre, France aboard La Bourgogne. He had only one bag and listed no final destination when he registered in New York (he listed his profession as “workman”). Perhaps he was going to see his young grandchildren, Edgar (3 years old), Alma (2 years old) and the newborn, Melitta. Regardless, Leo died in Vienna in 1917, age 71. His widow, Klara died in 1931, age 85, and is buried in the same plot.
In fact, there are four Kobaks buried in Vienna. In addition to Klara and Leo, David and Jakob Kobak are buried in the same cemetery. David died in 1898, while Jakob died in 1902. I do not know if they were related to Leo, I speculate that they were. And I imagine they were at least related to each other (brothers? father/son?) because they, too, are buried in the same plot as each other. I have no idea how old David and Jakob were when they died. Perhaps Leo’s journey to America in 1898 was also linked to the death of David (maybe it was his father?).
Kobak 