Mainly in cell nuclei .
In Eukaryotas
DNA means Deoxyribo##color(blue)(nucleic)## acid. The word nucleic is used because they were initially found in cell nuclei.
But there are DNAs in Mitochondrias and in Chloroplasts (in plants)
There are some other cell organelles called Plasmids which are actually parts of DNAs.
In Prokaryotas
In prokaryotas there is no organelle called nucleic(which is an organized one). The DNAs in these guys are circular and naked.
Here also are plasmids that are DNA parts.