Will Jews be judged under the law or the new covenant?
There is only one covenant in effect today. "Nor is there salvation in any other, for there is no other name under heaven given among men by which we must be saved" (Acts 4:12). Everyone is judged according to Jesus' teachings. "He who rejects Me, and does not receive My words, has that which judges him -- the word that I have spoken will judge him in the last day" (John 12:48).
Jews who lived under the Old Law before Christ came and died for mankind, will be judged by that law. A Gentile living before Christ's death will be judged what he ought to have been able to understand. "For as many as have sinned without law will also perish without law, and as many as have sinned in the law will be judged by the law" (Romans 2:12).
For more details see: Can a Jew go to heaven?