Can I ask Allah for death before Dajjal comes?
This is not permissible. Death is coming inevitably. However, one must not wish for it or make it an obsession. One must act normally and do good deeds and avoid sins so that when death comes, he would be anticipating it and welcoming it.
It was narrated from Anas ibn Maalik (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said: “No one of you should wish for death because of some harm that has befallen him, but if he must do that then let him say: ‘O Allaah, keep me alive so long as life is good for me, and cause me to die when death is good for me.'” Agreed upon.