'Who' has two forms: ngê ('person') and ngêi. It is not clear to me where the -i comes from; it could be derived from the distal demonstrative si 'that' or from the interrogative determiner kutxi 'which' (see Maurer 1995: 225, fn. 92).
There are two compound expressions for 'when': ola kutxi [hour which] and dia kutxi [day which].
Source: Maurer 1995: 138
Source: Maurer 1995: 138
Source: Maurer 1995: 138