What is the process that allows DNA to make copies of itself before cell division? Where in the cell does this take place?

DNA replication or DNA synthesis is the process of copying a double-stranded DNA strand in a cell, prior to cell division. In eukaryotes, this is during the S phase of the cell cycle, preceding mitosis and meiosis. The two resulting double strands are identical (if the replication went well), and each of them consists of one original and one newly synthesized strand.

DNA replication occurs in the nucleus.