The reason why ray-tracing is often used for achieving as-realistic-as-possible wet appearance is their reflective behavior. A thin liquid film on the surface reflects photons like a mirror. If you target real-time rendering, you will have to fake the reflections (or rely on RTX :) There are two ways I can quickly think of: placing reflection probes in the scene using cube-maps or using screen space reflections.
Reflection probes with cube-maps
- good for static scenes, you can pre-compute many of them
- allow objects outside of the current viewing frustum to be seen in the mirrors
- inaccurate due to limited number of probes
There is a great extensive tutorial by Sébastien Lagarde on reflections which continues (what a coincidence) with part B on wet surfaces and there is part C as well. Make sure to check them out!
- fine also for dynamic scenes
- only objects in the current viewing frustum can be seen in the mirrors
- accurate within the frustum
Screen space reflections are explained as part of this awesome series by David Lettier.
Regarding the discussion on subsurface scattering, any organic tissue exposes this property. We just observe it the most on skin or leaves, but the same effect is observed inside the body. Just read section 3.3 of this paper:
One significant casual effect under endoscopic environment is a strong subsurface scattering on the surface of internal organs.
I suggest to use at least some post-processing technique for that.