can_be_knight_trigger

can_be_knight_trigger = {
	is_available_quick = {
		ai = yes
		hostage = no
	}
	can_be_warrior_trigger = { ARMY_OWNER = $ARMY_OWNER$ }
	trigger_if = { # Admin governors cannot be knights
		limit = {
			$ARMY_OWNER$ = { government_has_mechanic = administrative }
			is_courtier = no
			exists = primary_title
		}
		primary_title = {
			tier < tier_duchy
			trigger_if = {
				limit = { is_noble_family_title = yes }
				always = no
			}
		}
	}
	trigger_if = {
		limit = {
			$ARMY_OWNER$.culture = {
				has_cultural_parameter = minimum_prowess_for_knights
			}
		}
		prowess >= 12
	}
	trigger_if = {
		limit = {
			is_clergy = yes
		}
		OR = {
			rite = { rite_has_parameter = clergy_can_fight }
			AND = {
				has_personal_tenet_flag = clergy_can_fight_personal
				NOT = {
					rite = { rite_has_parameter = pacifist }
				}
			}
			culture = { has_cultural_parameter = culture_clergy_can_fight }
			AND = {
				$ARMY_OWNER$.culture = {
					has_cultural_parameter = high_prowess_ignores_knight_restrictions
				}
				prowess >= 10
			}
		}
	}
	OR = {
		AND = {
			$ARMY_OWNER$.culture = {
				has_cultural_parameter = high_prowess_ignores_knight_restrictions
			}
			prowess >= 10
		}
		has_trait = order_member # Order Members will fight for their faith even if their faith says no
		NOR = {
			has_trait = blind
			has_court_position = master_assassin_court_position #FP3 addition
		}
	}
	trigger_if = {
		limit = {
			exists = liege.diarch
		}
		this != liege.diarch
	}
	# knight permissions for players
	trigger_if = {
		limit = {
			$ARMY_OWNER$ = {
				is_ai = no
			}
		}
		is_knight_permitted = $ARMY_OWNER$
	}
}

As written in game/common/scripted_triggers/00_war_and_peace_triggers.txt.