Does a woman receive a reward for wearing the niqab if the motive behind her husband's request for her to wear it is his desire to conceal her appearance to avoid people's talk due to his frequent divorces and marriages?

The ruling on niqab is explained in Fatwa no. 33957. A person is judged according to their intention. If you wear the niqab in compliance with Allah Almighty's command, you will be rewarded, regardless of your husband's intention. Similarly, obeying one's husband in matters that are not sinful is an act of worship for which one is rewarded. For further benefit, please refer to Fatwa no. 135267.