CEs for Enkidu?

I have several thoughts:
(a) solo game: you can have him CEs with guts, invulnerable, healing etc. to further improve his survivability,
(b) dual Enkidu: depends, I prefer more NP gain or star generation, or further improve his durability
(c) critical team for NP spam: I recommend to have NP gain CE but combo effect.
(d) normal critical team: star absortion CE for him, but imo, i dont really recommend this route, since he has none critical-up or attack-up skill, and 3 Quick cards still a burden in this case
(e) one punch style, with start-up NP or NP damage-up CEs, or attack-up, such as "Golden Sumo Wrestling"

I personally am not really recommend the Quick-up CE except there is CE with a good combined effect. He indeed has 3 Quick cards, but Quick-up can only slighly improve star generation and np gain (even mlb Imaginary Around) for him, because his Quick card isnt that good as Jack or Okita.

But I suppose you are playing JP for that pool, if you have Merlin+Skadi, then NP gain-up or NP damage-up are good choice. like "Cute Orangette", "Heading Towards Trifas", etc.
There are a lot of CE with combined effect. Like "Chaldea Lifesavers", is probably good in a solo game. depends.

Holy Night Sign sounds like the one that best suits what you're looking for.

Something a bit more niche would be "A Moment of Silence", (+10% arts/quick up, +10% NP gen up) but since that's a limited CE it's a bit harder to get.

I really think a buster up CE and/or an NP strength CE will serve you a bit better with Enkidu. He's a lot more consistent in that regard, especially with Merlin support.

Enkidu is incredibly versatile, so there are tons of CEs that can work for them. There isn't a best one, it depends on what you want to use them for.

Any CE that focuses on either Quick/Buster, Crit, or NP gain / NP damage (or all three / mix of some of these stats) should work.

The "Talk of the Hot Sands" CE from Chaldea Boys 2017 (the upcoming CB event in NA) seems like it'd make Enkidu crit like a beast and gather the stars they need instead of them going to another servant. You'd only need a star generator in the team for it to work, though.

For Buster: First Sunrise (Buster up + NP charge), or Golden Sumo, or hell, even Victor of the Moon if you have a star generator to give Enkidu stars to crit sound like good options. True Samadhi Fire or Heroine Eli-chan's adventure for +NP damage and Buster up.
Three of these CEs are from events, sadly.

For NP gain / NP damage: Halloween Princess, Heaven's Feel, The Three Great Heroes (bonus +% star generation), Holy Night Supper (bonus critical strength). Teacher and I for NP charge + star absorption.
Except Heaven's Feel, all are event CEs, though.
The Black Grail could work, giving Enkidu's ability to heal themselves by a massive amount + their incredibly high hp. But I personally don't like Demerits in CEs, so Heaven's Feel > The Black Grail, imo.

For Quick up, I have my own Enkidu with Innocent Maiden, actually (NP +4% each turn, Quick Card +10%. Not MLB yet) and it's been working well so far, for the time being...

But if you want to use Enkidu for their NP, Damage up/Buster up/Np damage + NP gain/charge is the way to go. For crits, Quick and/or critical strength + star generation/absorption.