I don’t really follow this exercise,but I’ll try to do it to the extent I understand.
1.Fe-1 we can see 4 fold rotation axis and two 2 fold rotation axis. That means that we know how the principal axes system looks like. About 4-fold axis will be symmetry for the field gradient, that means that n = 0.
2.Fe-2 we can see three 2-fold rotation axes. And therefore we can say what would be principal axes system. But we can’t say anything about n (Eta).