"who" (pronoun used for inquiry)

"to whom" (used in expressions or legal terms)

"कौन"

English Usage: "Cui do you think will win the match?"

Hindi Usage: "Cui आपको लगता है कि मैच जीतेगा?"

"whose" (used to ask about possession)

"किसका"

English Usage: "Cui book is this?"

Hindi Usage: "Cui किताब है यह?"