Only blue wands can be shopped, that is magic wands with only 1 prefix and/or 1 suffix.
You can expect +2 to necromancer skills and +20 fcr.
As for the staffmods, probably something like +3 to Clay golem, +3 to Summon res and +3 to Bone spear, the last being useful to raise your first skeletons.
For a rare wand that you would drop, you can take the same and add 2 random prefixes and 2 random suffixes.
Random prefixes : 40 fire res, 40 light res, 40 cold res ...
Random suffixes : nothing useful to be honest, maybe a bit more energy ?
Now if you try to roll (with p.skulls, or with p.skulls and SoJ), you can produce rare +2 wands with different staffmods, like +3 Raise skeleton, +3 Skeleton mastery.
Those 2 staffmods only spawn on iLvl 1-24 wands, that's why you won't see them on shopped or dropped wands, once iLvl is high enough to allow +2 class skill.