So say an Isengard troll has a defense of 8, and is charged by a strength 3 warrior, which means a 6/4 is required to wound.

Will that warrior get to roll 2 dice or will he need another attack to complete the second part of the wound?

_________________
Forlorn, I remove my Iron Guard from the pile of Goblins; just staring at that 6 with disbelief.

In that case warrior 1 has failed to wound but warrior 2 get to roll another die and try to get a 4+ in order to wound.

To wound 6/4 you roll one dice for each attack. Any dice that get a 6 need to be rerolled. If any of those gets 4+ you'll wound the troll.

If the warrior wields a 2h, you will only need to roll a 5/3. The 2h applies to both rolls as they both are dice to wound.

_________________
I cannot jump the distance, you'll have to toss me.
- Gimli, The 2 towers

If warrior A charges in and rolls a 6 for damage but then fails to roll a 4, the next warrior to charge in (warrior B) must still roll a 6 before he successfully wounds by rolling an additional four. Likewise if, say aragorn, needs to roll a 6/4 to wound something, and he rolls a 3 a 4 and a 6, this does not mean he wounded to critter. This means he has the opportunity to reroll the 6 and hope for a 4+ to wound the creature.