"Does anybody know what it is?" is correct. The other version isn't. I don't know the grammar, if that's what you are asking, sorry.

Hi Ruslan. To follow up on Gary's correct answer, if you really want to know, we don’t invert questions in subordinate clauses. It’s a rule. Sometimes we refer to these clauses as “embedded questions”. Actually, we don't need to use a question in the main clause either: "I wonder what it is" or "tell me what it is!" Basically, the subordinate clause is functioning as a noun, for example: "Does anybody know this fact?" or "Please tell me that fact!"