Specifically, the PRD says for Saving Throws Against Magic Item Powers in the Magic Items section:
Saving Throws Against Magic Item Powers
Magic items produce spells or spell-like effects. For a saving throw against a spell or spell-like effect from a magic item, the DC is 10 + the level of the spell or effect + the ability modifier of the minimum ability score needed to cast that level of spell.
Staves are an exception to the rule. Treat the saving throw as if the wielder cast the spell, including caster level and all modifiers to save DCs.
Most item descriptions give saving throw DCs for various effects, particularly when the effect has no exact spell equivalent (making its level otherwise difficult to determine quickly).
For the caster level, under Determine Effect in Scrolls PRD entry it says:
Assume the scroll spell's caster level is always the minimum level required to cast the spell for the character who scribed the scroll, unless the scriber specifically desired otherwise.