A warlock with +1 Rod of the Pact Keeper wants to cast a spell into a ring of spell storing while attuned to the rod. The rod provides a plus one to her spell attack and spell save DC. Are these bonuses from the rod conferred onto the spell in addition to her innate spellcasting modifiers when it is released from The Ring of Spell Storing?
It's not clear how stored spells should work with situational bonuses
The Ring of Spell Storing states:
[...] The spell uses the slot level, spell save DC, spell attack bonus, and spellcasting ability of the original caster, but is otherwise treated as if you cast the spell. [...]
So we need to determine what are considered to be your spell save DC and your spell attack bonus.
Your spell attack modifier is defined as follows (from the wizard class and the chapter on Spellcasting):
Spell attack modifier = your proficiency bonus + your Intelligence modifier
Your attack bonus with a spell attack equals your spellcasting ability modifier + your proficiency bonus.
Note, it does not say that situational pluses and minuses change your attack bonus. Thus, it would seem that Rod of the Pact Keeper does not impact your attack bonus; instead, it gives you a bonus to your attacks, similar to the bless spell.
Meanwhile, your spell save DC is defined (from the same places) as follow:
The DC to resist one of your spells equals 8 + your spellcasting ability modifier + your proficiency bonus + any special modifiers.
Spell save DC = 8 + your proficiency bonus + your Intelligence modifier
In this case, the general rule actually does mention that special modifiers impact the actual save DC value. And while I do think it would be unusual to have the Rod of the Pact Keeper affect the save DC of stored spells but not their attack bonus, that is how it seems to be written.
A GM can always rule however they like
A GM is well within their rights to say that the Rod of the Pact Keeper applies to both your attack bonus and save DC or even that it applies to neither. They should probably keep in mind that this would mean any other situational modifiers (for example, from the resurrection, raise dead, temple of the gods, bless, and synaptic strike spells) similarly would or would not apply to stored spells.