When a question word is repeated, it indicates that the expected answer is to be a list of things.
ਜਾਣ ਤੋਂ ਪਹਿਲਾਂ ਕੀ ਕੀ ਚਾਹੀਦਾ ਹੈ ਤੁਹਾਨੂੰ?
jāṇ to(n) pahilā(n) kī kī chāhīdā hae tuhānū(n)?
Before going, what (plural) do you need?
jāṇ to(n) pahilā(n) kī kī chāhīdā hae tuhānū(n)?
Before going, what (plural) do you need?
Because kī (what) is repeated, the expected answer is a list of things
ਕੌਣ ਕੌਣ ਆਇਆ ਸੀ ਅੱਜ?
kauṇ kauṇ āiā sī ajj?
Who (plural) came today
kauṇ kauṇ āiā sī ajj?
Who (plural) came today
Because kauṇ (who) is repeated, the expected answer is multiple people
ਕਿੱਥੇ ਕਿੱਥੇ ਜਾ ਕੇ ਆਇਓ ਕੱਲ੍ਹ?
kitthē kitthē jā kē āio kallh?
Where (plural) did you go to yesterday? (lit. Where did you go and come back?)
kitthē kitthē jā kē āio kallh?
Where (plural) did you go to yesterday? (lit. Where did you go and come back?)
Because kitthē (where) is repeated, the expected answer is multiple places
This repetition does not always work for every question word. kiu(n) kiu(n) (why why) for example is not used