Original spelling of the surname is STOJKOVSKI ( in Cyrillic alphabet : СТОJКОВСКИ ).
That family in period records is listed as ethnic Macedonian and of Eastern Orthodox faith.
Use the original spelling in both variants if you are trying to locate via social networks like facebook people with same surname from Macedonia who might be your relatives and able to help you with your research.
I cannot give you any more advice without knowing and confirming the place of birth or last residence of your father - try to obtain a record or a document that has that information from his life after emigrating.
"Rodoslovlje" Serbian Genealogy Societywww.rodoslovlje.com