A fascinating question, really!
To some degree, it depends on personal working style and the jewelry
one is creating. There are goldsmiths who largely do repair work, sit
at a workbench all day every day doing soldering (hard on the eyes)
and setting (hard on the eyes, primarily) and not a lot else... they
need good hand strength, good eyes, ability to sit in a relatively
fixed position for long periods of time, etc.
For others, it's a much more physical endeavor. If one is doing
forging, you're standing, hammering, moving, etc. For using a rolling
mill (if it's a manual one), you may need a bit of arm and back
strength to turn the handles (while standing). Hydraulic press can
require the ability to pump a handle in a motion similar to using a
car jack (also standing). Casting requires a different set of
physical skills, including reaching into a blazingly hot oven to
remove (with tongs) a heavy flask, place it into a centrifuge, then
melt the metal for the casting. You then have to remove it from the
centrifuge (again, with tongs) and quench it.
For myself, I've set up my home studio (and the one at school to a
large extent promotes this as well) to get me OFF my butt. Sometimes
I work standing up, and I certainly have to move between my soldering
station, my pickling area, and my bench area. That way, I'm not
tempted to "park it" for hours at a time.
I suspect you'll get lots of different answers to this one, but I
can tell you that the physical capabilities I value the most are my
eyesight, my hand strength/flexibility, my arm strength/flexibility,
and my back.
Hope this helps you understand some of the physicality of the work!
No Limitations Designs
Hand-made, one-of-a-kind jewelry