Advancement with Entity NBT (custom Name) and How to Test

{
"display": {
"icon":

{ "item": "minecraft:diamond_axe" }

,
"title": "Independent",
"description": "Defeat The Knight",
"frame": "goal"
},
"rewards":

{ "experience": 50 }

,
"criteria": {
"ires": {
"trigger": "minecraft:player_killed_entity",
"conditions": {
"entity": {
"type": "minecraft:zombie",
"nbt": "

{CustomName:\"Dark Knight\"}

"
}
}
}
}
}

I'm really Sorry For similar Question...
I've searched a lot, But can't solved any issues.

also, how can I test it?
Tried /summon zombie ~ ~ ~

{CustomName:"\"Dark Knight\""}

and kill zombies but but Doesn't work.

use Mythicmobs and Named Dark Knight, Kill, but It didn't work too....