The name of the compound NiSO4 • 5H2O is nickel (II) sulfate pentahydrate. Since there is a transition metal cation with multiple oxidation states, you have to include the Roman numeral in the brackets.
Ni is nickel, so the first part is obvious. Since there are four equivalent oxygen atoms in a tetrahedral arrangement, it is also a sulfate. Penta refers to number 5, and hydrate because it consists water.