Kate
I believe that was a typo and may have been referring to someone I found in the 1910 US Census in Cleveland Ohio. The 1930 census states he arrived in the US 1905.
While there are several possible matches for him in US Immigration records the closest based on what he gave in his WW I Draft Regristation with his birthplace being Karlstadt would be a Stefan JANKOVIC arriving in the US 1905 from Karlovac .... Karlstadt was the Austrian name fro Karlovac
There are 32 listings in Karlovac County phone book for JANKOVIĆ
Also I notice that his military paperwork he stated that he had previously served in the US Military. I find an earlier military record Name: Steve Jankovich
Event Type: Military Service
Event Date: 15 Dec 1910
Event Place: Columbus Barracks, , Ohio, United States
Age: 21
Birth Year (Estimated): 1889
Volume Number: 128
Page: 225
https://familysearch.org/pal:/MM9.3.1/TH-1942-26471-35505-29...But a key piece needs to be found... and that is his Naturalization Papers.... these ought to give his birthplace You may be interested in our Croatian Heritage and Genealogy Facebook Group
https://www.facebook.com/groups/1491621441073063/Robert Jerin
Croatian Heritage Museum
Cleveland Ohio