Rod of the Pact Keeper +2 gives a "+2 bonus to spell attack rolls and to the saving throw DCs of your warlock spells." So it only applies to Warlock spells, if you have spells from another class it doesn't apply.
So a warlock Pact of Tome grants three cantrips from any spell list. So on the face of the Rod of the Pact Keeper description, it initially seems the bonus does not apply if those cantrips aren't warlock spells. And that is how it's calculated on my sheet: Vicious Mockery (not on Warlock list) is 8+5(Chr)+4(Prof) = 17, and Mind Sliver (Warlock list) is 8+5+4+2(Rod)=19.
However, the text of Pact of Tome says "If they don’t appear on the warlock spell list, they are nonetheless warlock spells for you," which was confirmed in the PHB errata 1.1. So those cantrips I get through my Pact Boon are counted as warlock spells and should receive the Rod bonus.
This is a known issue since 2019 it seems, and still no fix
Rod of the Pact Keeper +2 gives a "+2 bonus to spell attack rolls and to the saving throw DCs of your warlock spells." So it only applies to Warlock spells, if you have spells from another class it doesn't apply.
So a warlock Pact of Tome grants three cantrips from any spell list. So on the face of the Rod of the Pact Keeper description, it initially seems the bonus does not apply if those cantrips aren't warlock spells. And that is how it's calculated on my sheet: Vicious Mockery (not on Warlock list) is 8+5(Chr)+4(Prof) = 17, and Mind Sliver (Warlock list) is 8+5+4+2(Rod)=19.
However, the text of Pact of Tome says "If they don’t appear on the warlock spell list, they are nonetheless warlock spells for you," which was confirmed in the PHB errata 1.1. So those cantrips I get through my Pact Boon are counted as warlock spells and should receive the Rod bonus.
This is a known issue since 2019 it seems, and still no fix
https://www.dndbeyond.com/forums/d-d-beyond-general/bugs-support/34700-rod-of-the-pact-keeper-not-effecting-warlock-bonus
You can fix it by going into the affected spell customization and adding the +2 to DC or To Hit manually.