The nashorn can see through only 1 hex. That means you can ignore the obstruction, whatever it is(forest, city, mountain, etc). If the enemy is behind 2 hexes of obstruction, then it is no good.
You can find revised cards through Eastern Front here. Revised cards have a ribbon in the lower right hand corner of the card. Hope this helps.
The “spotting range” requirement is usually listed on the attacking unit. You go by whatever it says, barring any other ruling or effect.
SS-Jagpanzer Extended Range 12
Jagpanzer (1944) Ext. Range 12
Jagdpanzer IV L/70 No ext. range
Jagdpanzer IV/48 (1944) No ext. range
Jagdpanzer 38 T (Hetzer) No ext. range
STUG III G No ext. range
STUG III D No ext. range