How to achieve this shiny effect on the sponge surface in Cycles? The sponge shows tiny speckles reflecting light.
Add an RGB Curve to gain more control. The right of the curve will control the roughness of the tiny spots : I set it to 0.0 so they will be really shiny. The left of the curve will control the roughness of the base material ; If you set it to 1.0, it will be totally diffuse ; I recommend some intermediate value, around 0.75 or higher, but it's your move.
Finally, connect this into the Roughness slot of a principled BSDF and tweak the other values to fit your needs (some Transmission should look good, maybe even some Subsurface). Once it's done, you'll probably want to adjust the RGB Curve a bit.