I’m playing a paladin of conquest and am often casting spells or effects that require enemies to make a saving throw against my spell save dc. Can I add my aura of protection bonus to the spell save DC, making it 8+proficiency bonus+Charisma modifier+aura of protection bonus?
Aura of Protection
Starting at 6th level, whenever you or a friendly creature within 10 feet of you must make a saving throw, the creature gains a bonus to the saving throw equal to your Charisma modifier (with a minimum bonus of +1). You must be conscious to grant this bonus. At 18th level, the range of this aura increases to 30 feet.
Note how this only affects saving throws, as opposed to your spell saving throw dc. Since it affects only friendly creatures, it won't affect an enemy, so they will never be affected by Aura of Protection.