Irreducible tensor operators as the irreducible submodules of an adjoint representation of the two-parametric quantum ∗-algebra [Formula: see text] are constructed by using its Jordan–Schwinger formulation on two independent [Formula: see text]-oscillator ∗-algebras. All [Formula: see text]-submodules are equipped with an appropriate Hilbert–Schmidt scalar product with the help of the Wigner–Eckart theorem. We show that with respect to this scalar product, not only the bases of all irreducible submodules of the adjoint representation are orthonormal, but also the adjoint representation is a ∗-representation.