Adam and Eve are the parents of Abel and Cain. Who is Cain’s wife?
In Genesis 4:17, after Cain is given a mark to protect him, the Bible simply says that he knew his wife and she bore Enoch. But some people understand the Bible to say that only Cain and Abel were born to Adam and Eve at this point.
However, in most situations the Bible doesn’t record the daughters that are born. It also doesn’t tell you all of the sons that are born. After the garden, Adam lived for 930 years. I can assure you that he had many children with Eve.
The Bible mentions the sons and daughters that are important to the story of what God is doing. It doesn’t record everything that ever happened in history. So Adam and Eve had more sons and daughters then just Cain, Abel, and Seth.
Although the Bible doesn’t describe these children, they would also have had children of their own. So Cain’s wife would have been either a second or third generation human. The Bible doesn’t describe where these people went after they were born either. Cain goes somewhere else other than where the rest of the family of Adam and Eve are. He was banished from that place.
But he would’ve gone to another place where the other people who originated from Adam and Eve lived. Humans were told to spread out and populate the earth (Genesis 1:28). The humans on the Earth would have spread out and Cain found one of these other groups.