On the weapons table in fantasy hero it has a Battle Axe that does 2d6 damage with the Notes stating 1 1/2H.  How much damage does it do one handed?

The damage is the same, but using a 1½ handed weapon with only one hand increases the STR Minimum for the weapon by +2, or imposes a -1 OCV penalty. See 6E2 200 for the rules on "handedness" for weapons.