Even though we write the name using the English alphabet - apparently the original spelling is Đoković - we normally follow the pronunciation in the original language. For interviewers and sports commentators, they do try to say the name as in the original language. Anglicising the name just sounds tacky and ignorant, especially at international level.

It's pronounced more like 'ch'. As for why, it's because the name isn't English/Anglo-Saxon. It's a Slavic name, and Novak Djokovic is Serbian.

It's a Slavic name, so the 'c' it's pronounced like 'ts'.