What is the server command to give my named wolf more health in Minecraft version 1.16

Directly, I don't think it is possible to increase an already spawned mob's health without help of a world editor.

Indirectly, you can give yourself a custom, infinite duration healthboost-effect splash potion with the following command from the Minecraft Tools potion generator:

/give @p minecraft:splash_potion{Potion:"minecraft:water",CustomPotionEffects:[{Id:21,Amplifier:127,Duration:2147483647}],display:{Name:""Custom Potion""}}

This is a command that will give you a splash potion with the max level of health boost, being 128, with each level increasing the mob's health by 2 hearts (4 points of health).

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And although this part probably doesn't answer your question, I'll include it for broadness, you can also just summon a wolf with more health using this command:

/summon Wolf ~0 ~1 ~0 {Attributes:[{Name:generic.maxHealth,Base:500}],Health:500.0f}

With "500" being an adjustable number, though bear in mind that 1024 is the maximum amount of health points a given mob can have.