I am 36 and i desperately want to have sex with my elder sister, I do not know how do I ask her for sex, atleast I would like her to strip infront of me. How do I ask her to strip. Please help

I suppose you could create a situation where she can see you "accidentally" naked first. Maybe you come out of the shower and your towel falls down, maybe she walks in on you masturbating, or you could even leave naked photos of yourself out in a place where she could see them. Situations like those will help you break the ice, and allow you to gauge her reaction, so that you can get an idea if she might be interested. If she reacts in a positive, or at least not negative way, then maybe you could open a dialog with her and tell her what is on your mind.