1) May I know how will it differs for composite field ONB? Does it takes two ONB fields to construct a valid ONB composite field? Or not necessarily?

eg: both GF(2^n) and GF(2^m) are ONB1 and then it is possible to have GF((2^n)^m) which is composite field ONB1?

2) How do I check if a field is ONB 2 or not? Eg: GF(2^41)