You put some under a microscope, count the spermatozoa per drop, and count the number of wigglers. On the other hand, consider samples of rabbit brain tissue studied for coordinated electrical activity after perfusion with glycerol and rewarming from liquid nitrogen temperature. One of the broad-brush variety is just to culture cells and see if they grow and reproduce. I doubt that anyone yet can say which is the most important or which are essential for recovery without nanotechnology. I'm not looking a gift horse in the mouth.
Progress is welcome, even if there is still a long way to go.
I'm just trying to get some perspective. Much more extensive background is available elsewhere on this web site.