The correct option is: C
In a cyclic quadrilateral, opposite angles add up to 180 degrees. If the angle JFG is 56 degrees, it would prove that quadrilateral FGHJ is inscribed in Circle O.
In a cyclic quadrilateral, opposite angles add up to 180°.
So, if m∠JFG = 56°
m∠GHJ + m∠JFG = 180°
m∠GHJ: m∠GHJ + 56° = 180°
m∠GHJ = 180° - 56° = 124°.
Therefore, the correct option is: C m∠GHJ = 124°.