Which one of my CE is best for Jack?

Holy night for quick and crits strenght
Knights for 50% Np and quick
Dangerous beast gives more quick strenght and passive stars so you can use it intead of Holy night (?
It depends on your team composition

Jack doesn't really need knights of marine because she charges np really quick unless you use waver for 1st turn np.

Imaginary around is usually preferable because of the whopping 25% quick up.

Holy night sign is good if you don't have someone with higher star weight to take the star away from jack, though imaginary around might still give more power with her quick deck (8% isn't much compared to 25%)

I'm not familiar with dangerous beast.

Imaginary Around is the single best CE for Jack in most situations, lacking that the next best option is MLB Grandr, If you don't have MLB Grandr, Dangerous Beast works decently. Unfortunately Holy Night sign just isn't very good until MLB, Kights of Marine is okay if you are doing turn 1 NP stuff but not great outside that.