I mean
I know how to add my own recipes (and I have added them *for example:
{
"type": "draconicevolution:fusion_crafting",
"catalyst": {
"item": "mekanism:electric_pump"
},
"ingredients": [
{
"item": "mekanism:upgrade_speed"
},
{
"item": "mekanism:ultimate_control_circuit"
},
{
"item": "mekanism:upgrade_energy"
}
],
"result": {
"item": "ad_astra:water_pump"
},
"tier": "WYVERN",
"total_energy": 10000000
}
*for this script i use kubejs data folder

but I don't know how to add a recipe that requires *example: 64 wither skeleton skull per slot to craft nether stars

can i ask how to do it?

You can only use stack size greater than one in the catalyst slot. Injector ingredient stack size is only ever 1 item.