It's not clear if I get the bonus for the hex I'm in or for the hex I'm attacking.

Example - I have some light infantry in woods, attacking an adjacent enemy in clear. Do I get the +3 bonus for being "in rough terrain" or do I have to be attacking an enemy that's in rough terrain?

Also, when the enemy counter attacks, will I gain the +3 woods bonus for being in rough terrain, or does this only count when you are the active attacker and not on defense?

The answer will make a big difference in my playstyle, that's for sure.

I'm also wondering this. Looked at the whole manual and couldn't find a definite answer. But in similar wargames the battle is assumed to happen at the defender's hex, so that's what I'm going with.

If this question is about FG1, then that's correct. The terrain of the defending unit is what counts when determining terrain bonuses.