The classical example of a Grothendieck space is $\ell_\infty$. It is also known that its even duals $\ell_\infty^{**}$, $\ell_\infty^{(4)}$, $\dots$ are Grothendieck spaces.
(See, e.g., this note for the proof of the Grothendieck property of these even duals, which uses the fact that these spaces are $C(K)$ spaces for large Stonian $K$-s.)
Is it known, in general, whether the second dual of a Grothendieck space is a Grothendieck space too? Is there a counterexample?
Edit (T. Kania). Let me record here for the future reference that this very question was asked by J. Diestel on p. 105 in
J. Diestel, "Grothendieck spaces and vector measures", Vector and Operator Valued Measures and Applications, Acad. Press (1973) pp. 97–108.