{{/give @p skeleton_horse_spawn_egg{EntityTag:
{id:"minecraft:skeleton_horse",Health:75f,Attributes:[

{Name:generic.max_health,Base:75}

,

{Name:generic.movement_speed,Base:0.47}

,

{Name:generic.armor,Base:15}

,

{Name:generic.scale,Base:6.1}

,

{Name:generic.step_height,Base:6}

,

{Name:generic.armor_toughness,Base:3}

,

{Name:"generic.follow_range", Base:100.0}

,

{Name:"generic.knockback_resistance", Base:0.4}

],Passengers:[{id:"minecraft:skeleton",Health:100f,CanPickUpLoot:1b,HandItems:[{id:"minecraft:bow",Count:1b,tag:{Enchantments:[

{id:"minecraft:power",lvl:5s}

,

{id:"minecraft:punch",lvl:2s}

,

{id:"minecraft:flame",lvl:1s}

]}},{}],Attributes:[

{Name:generic.max_health,Base:100}

,

{Name:generic.movement_speed,Base:0.52}

,

{Name:generic.attack_damage,Base:25}

,

{Name:generic.armor,Base:10}

,

{Name:generic.scale,Base:6.1}

,

{Name:generic.step_height,Base:6}

,

{Name:generic.armor_toughness,Base:2}

,

{Name:"generic.follow_range", Base:100.0}

,Name:"generic.knockback_resistance", Base:0.5}]}]}} 1}}

Use the spawn egg and it gives a giant skeleton horse without the indicated passenger, which is a giant skeleton with an enchanted bow. The spawn egg is expected to spawn a skeleton horse with the skeleton as the passenger. This also applies to other commands such as the following:

{{/give @p ravager_spawn_egg{EntityTag:{id:"minecraft:spider",Passengers:[

{id:"minecraft:skeleton"}

]}} 1
}}