I need help

You can look it up on SWGOH.gg

https://swgoh.gg/characters/?ac=armor_shred

Obviously, it depends on what you have.  Also, where you want to farm the feat.  The difficulty tends to be killing them too quickly.  However, Mandalorians are a good team for it.  Bo-Mandalore, Armorer and OG Sabine all apply armor shred.

To find out which characters apply it.  You can search engine swgoh.gg armor shred; this will give you a list of characters that do it.

Sabine Wren is good, or if you have Fennec Shand also. Can do the Chewbacca event with Fennec over and over

Moff Gideon- dark saber armor shred. 
Sabine Wren phoenix squad - dark saber armor shred
The Armorer - Armor shred attack

These got me 50 in about 20 minutes.

They 99% likely don't have Fennec if they're asking about what armor shred is and how to do it. Fennec is granted in another lightspeed token once you get through others, so very unlikely. As someone who started new, their best options are Moff Gideon, Sabine Wren, The Armorer. 

I think too many people here forget that if they're asking how to do stuff for a lightspeed token, they very heavily likely do not have these journies unlocked (level 85 for chewbacca) or the characters you're suggesting. Always gotta think in the spot of a newer player and what they have unlocked.

Open your character tab, click on the first filter, go to the text field, enter the skill you are looking for, hit confirm, the game will filter all toons with the skill you are looking for.