Where does “-ज” come from?

-ज (Sanskrit) comes from Sanskrit जन्, from Proto-Indo-European ǵenh₁- — to produce, to beget, to give birth.

Ancestry of “-ज”, step by step

Step	Language	Word	Meaning
1	Sanskrit	जन्	class 1; to generate, beget, produce, create,...
2	Proto-Indo-European	ǵenh₁-	to produce, to beget, to give birth

-ज — Etymology, Origin & Word History | Etymology Explorer