You can’t use ce que in this sentence, it would be wrong:

Wrong: Je ne sais pas ce que vous parlez.

Here are correct sentences with translations, I hope they help you to understand the difference:

Je ne sais pas ce dont vous parlez. => I don’t know what you are talking about.

Je ne sais pas de quoi vous parlez. => I don’t know what you are talking about.

Je ne sais pas de qui vous parlez. => I don’t know whom you are talking about.

First two sentences are correct but ce dont is more elegant (and would be used when written), and de quoi is more common in conversations.

ce qui or ce quoi cannot be used in your example.