A snobbish elf Wizard/Druid walks into a tavern with a shield and staff of power.
He casts lightning bolt (VSM) at a drunkard drinking cheap domestic ale.
Then he casts a profanity laced thorn whip (VSM) at the goblin handing out the cheap stuff.
Does it apply for a Druid spell if it requires a Wizard to attune? (DM has ruled it qualifies as a Druidic focus.)
The bartender quickly hands him a bottle of foreign wine.
But the observant wizard scowls noting the wine was not appropriately chilled. He calmly stows the staff in his shield hand (Mearls?) and cast ray of frost at the terrified bartender to teach him a lesson.
Should the wizard get the bonus if the DM rules he can stow it in his shield hand?
To which of these spells/cases would this section of the Staff of Power apply?
While holding it, you gain a +2 bonus to Armor Class, saving throws, and spell attack rolls.
Answers should especially address the case where the staff is temporarily stowed in the shield hand.