Where does “サンダカン” come from?

サンダカン (Japanese) comes from Malay Sandakan, from Malay -kan, from Proto-Malayic *-kən.

Ancestry of “サンダカン”, step by step

Step	Language	Word	Meaning
1	Malay	Sandakan	—
2	Malay	-kan	Used to indicate transitive imperative verbs;...
3	Proto-Malayic	*-kən	—