who = suma
where = (o-)pe
when = (o-)ten
how = fa
The variant ope is archaic, pe is the normally used form. Compound status of oten ist questionable, since similar forms exist with o fara 'how far', o bradi 'how wide', o langa 'how long', o hei 'how high'.
Source: Wilner 2007
Source: Wilner 2007
Source: Wilner 2007
Source: Wilner 2007
Source: Wilner 2007