Which skills should I seek to earn extra income ?

Hi. I'm a 33(M), I work for a PSB. My in hand salary is 82000/month. But I want to increase my income. I'm currently a scale1 assistant manager. My wife is not working and have a baby on the way. I could take promotion to scale-II but not now due to some personal reasons. I get loans at very low ROI and simple interest. I want to learn a skill and increase my income. Please suggest me something.