DNA replication occurs in the nucleus of eukaryotic cell. By definition, prokaryotic cells do not have nuclei. Therefore, DNA replication occurs in the cytoplasm of a prokaryotic cell.
DNA replication is when DNA makes another copy of itself. DNA replication is needed in order to maintain the number of chromosomes that is characteristic to a species during cell division. During cell division, one parent cell divides into two daughter cells. If DNA replication did not occur, then the daughter cells would receive only half the number of chromosomes characteristic of that species.
Prokaryotic cells divide by binary fission. The DNA of a prokaryotic cell replicates during this process.