What is the punishment or is there any punishment for killing someone who has murdered, repeated acts of pedophilia, rape, etc. and someone who has destroyed Jews? like Yael killing the king in her tent during war to prevent more Jews being destroyed, can we do this in this day and age with terrorists, attackers of Jews, etc. ?

Shalom. Although the death penalty is mentioned in the Torah for severe crimes, the Talmud tells us that the threat was almost never carried out, but mainly serves as a way to stress the severity of those actions. That is regarding the halachic judicial system, which anyway cannot be carried out today because we have no Sanhedrin. On the other hand, Jewish law grants the government, whether it be a king or democracy, the option and even the obligation to use whatever measures are necessary in order to insure law and order, and to deter the individual villain or national enemies. This would include the death penalty and even going to battle, if it would limit and deter evil. Without a doubt, the government of Israel is too lenient regarding terrorists and their supporters who constantly threaten and attack Jews, and should use more power and pressure to deter our enemies and return our kidnapped (Rambam, Guide For the Perplexed, III, ch. 35). This should obviously be done by the State and army and not by individual vigilantes who just cause anarchy and actually distract the government and army from fighting the real enemy. The act of Yael is a shining example which the rabbis praise immensely (Talmud Nazir 23b), as an act of heroism at time of war, where killing the enemy general is actually considered a moral and praiseworthy action. With Love of Israel, Rav Ari Shvat