It’s possible for people or weapons to have 2 or more damage/extended tasks effects on a task or damage roll.

Suppose that you rolled 5 effects with challenge dices. Do you have to split the 5 effects between the 2 damage effects/talents or each one have 5 effects to use

No splitting of the rolled Effects, every rolled Effect triggers the quality.

For each type of Quality/Damage Effect:
(Number of Effects rolled) x (Rank of Quality/Damage Effect) = total applicable effect

If you have, for example, a Damage Effect of a weapon of Piercing 2 and Vicious 1, and you rolled 5 Challenge Dice resulting in 5 Effects, that would mean:
5 times 1 damage (the base damage of a Challenge Die showing an Effect symbol)
5 times Piercing 2 = Piercing 10 to ignore Resistance.
5 times Vicious 1 = +5 Damage to the usual total.
for a total of: 10 damage, Piercing 10

A single Effect rolled activates ALL qualities that are depending on the number of Effects.
All at once.

For each Effect rolled, those qualities are activated multiple times. This is cumulative.

If you have a quality of Piercing 2 and you rolled 3 Effects, that would activate this quality and you multiply the quality value times the number of Effects, so Piercing 2 x 3 = Piercing 6 total.

If you have multiple qualities like Piercing 2 and Vicious 1, and you rolled 3 Effects, EACH of those qualities are activated at the same time. And EACH of those qualities are activated with the multiplier of the number of Effects you rolled: Piercing 2 x 3 = Piercing 6, Vicious 1 x 3 = +3 damage.
You apply those evaluated Effects to the rolled damage total. In the example above it would mean the damage total gets +3 damage to the rolled total, and it gets the Piercing 6 to punch through Resistance.

You do not “split up” Effects to activate different qualities that are triggered by Effects.
So on a roll of 3 Effects for damage with Piercing 2 and Vicious 1 qualities, you don’t need to decide to split 1 Effect off to activate Piercing 2 for a total of Piercing 2 and 2 Effects to activate Vicious1 for a total of +2 damage.
ALL get activated the same time.
ALL get activated as often as the number of Effects you rolled.
No splitting up Effects, no distributing Effects to single qualities.

Maybe some reference to the STA rules book helps, emphasis mine:
p178:

When one or more Effects are rolled, all Damage Effects that apply to that attack are triggered.

p179:

PIERCING X: The Attack ignores X points of the target’s total Resistance for each Effect rolled.
VICIOUS X: The Attack inflicts X additional damage for each Effect rolled.