The ionic compounds on dissolving in aqueous solution dissociate into their respective ions that are cations and anions.
The ions present in the aqueous solution of [tex] CuSO_4 [/tex] are [tex] Cu^{2+} [/tex] and [tex] SO_{4}^{2-} [/tex].
So, the chemical formula of the cation present in the aqueous solution of [tex] CuSO_4 [/tex] is [tex] Cu^{2+} [/tex].