'Jak dobře znáš ji' - please, explain what is wrong here?
The "ji" is a clitic, so it has to be the second element in this sentence. The first one is "jak dobře - how well". Jak dobře ji znáš?
Thank you very much!
Can kolik be used instead of jak?
Not really. You are asking about the quality of the "knowing". Not for any specific measure.