I suspected someone is using witchcraft power against me and also after my life in the dream. Can I kill him/her?

Do not intend it let alone carrying out such barbaric act at all. Our law in Nigeria does not recognize Juju and witchcraft. If you kill someone on this ground, you will be charged for murder and may end up being executed too. We advice you either pray for or against such witchcraft power depending on what your faith/belief provides in this situation.