This question already has an answer here:
Enhance Ability (PHB 237) is a 2nd level spell granting either temporary hitpoints or advantage on any one of the 5 core skills (Str,Dex,Int,Wis,Cha).
It has already been answered several times that Initiative is a Dexterity check and as such benefits from advantage on such checks, like Cat's Grace would bestow from Enhance Ability.
I am wondering now about other types of d20 rolls: namely, can a Wizard gain advantage on spell attacks with Fox's Cunning? A rogue or fighter on their weapon attacks with Bull's Strength and Cat's Grace? A cleric or sorcerer on spells with Eagle's Splendor or Owl's Wisdom?
N.B. I am not concerned about the balance of this, only whether it is permissible based on the rules.