I want to check the trim condition for aircraft. For this I need the pitching moment coefficient of wing. How to calculate?
Take the pitching moment coefficient of the wing's airfoil at the trim angle of attack. Since the reference area normally is the wing's area and the reference chord is the wing's mean aerodynamic chord, you do not even need to adjust the number. I hope you have the airfoil polar at hand; if the wing uses several airfoils, take a volume-weighted average; volume being here the product of local area and chord. If the wing has a symmetric airfoil, the coefficient is zero, in most other cases it will be a small negative number.
Use XFLR5 to construct and simulate your a/c model. Adjust the inertial masses such that you achieve a trim angle in the acceptable region.