ko-ko- को को: Repetition of the interrogative particles. We use the repetition to express the fact that the answer has a plural meaning. The same process exists in languages such as Mongolian (from the same author: Introduction to the Mongolian Language - www.voyagemongolie.com).
Who is in your family??
Which languages do you speak?
Who is at your home?
What things are available in this shop?
On which days does Nepal have holidays?
How often do you take a bath?