How are we able to see a specimen on the stage of a microscope when no light is reflected from the specimen?

Well there are multiple types of microscopy. I ume you're talking about a bottom lit microscope. In that case, they're usually only used to view single celled specimens such as bacteria or blood cells. The reason why you can see them is because the light actually pes through the specimen. Single-celled organisms are generally translucent (meaning they can be partially be seen through). Thicker organisms or more opaque ones would require a top lit specimen.