I wanted to know
what different between dolphin skin and shark skin

Well a dolphin is a mammal and a shark is a cartilaginous fish so really there are an awful lot of differences between their skins in terms of their structure and function.

In a nutshell dolphins have a smooth skin which (unusually for mammals) is hairless. I believe the skin is so smooth in part because old skin cells are being continuously sloughed off and replaced.

Shark skin is rough (almost like sandpaper) and covered in tiny "scales" that are really more like teeth than the scales you find on most (ie bony fishes). These scales/teeth are called dermal denticles.