There is no indication of which town in North Borneo it originated from. If it was commercial mail, the letter would have been written on board ship or at least posted while it was in North Borneo waters bound for Singapore. It has a clear transit Singapore cds date of 16 NO 1931. The paquebot cancellation is a commoner type from Singapore. But with a North Borneo stamp on cover, it is still not that easy to find.
The ship involved here was most likely the SS Darvel. It arrived at Sandakan on 7 November and sailed on the 9 November bound for Singapore via ports eg Kudat, Jesselton and Labuan. The other 2 ships which also served this route were the SS Kajang and the MV Marudu.
Source: “My North Borneo Stamps” Blog and here exhibited kindly permissed by the owner.