So is this Homework assignment as suggested by the thread category? Assuming as such, readers are likely to provide clues to help the student figure out the solution(s) by themselves. In this particular case, the clues will probably be along the lines of Fortran lacking “jagged arrays” and what it can mean in terms of copying the data from the C pointer to a C char [][]` array obtained by the function call.
Depending on what your assignment requires, you may be able to pursue other options as shown here: Iso_c_binding: interface to a C function returning a string - #13 by FortranFan