Your caster level is based on the number of level in the spell casting class. If you are an 11th level wizard your caster level is 11. Unless you have some way to boost your caster level you cannot cast the spell at a higher caster level. There are ways to boost your caster level. The most common way to boost your caster level is with magic items. There are some feats and traits that can also boost your caster level, but those are often limited on what they can be used with. Anything that boosts your caster level will help with spell resistance as long as it applies to the spell being cast.
The feats spell penetration and greater spell penetration are the easiest way to help overcome spell resistance. Elves also get a +2 bonus on their caster level to overcome spell resistance, which stacks with spell penetration. A Robe of the Archmagi gives you another +2 bonus to overcome spell resistance. An Orange Prism Ion stone gives you a straight up +1 caster level.
|Taja the Barbarian|
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OP, is your character multi-classed? 11th level characters generally shouldn't be encountering SR 31+ foes routinely, as this is basically immunity to casters.
There are a number of traits that boost your caster level but are still capped by your character level, so they basically help multi-classed characters a bit. For example, my bloodrager 11 / Spriritualist 1 has an the following alternate Half-Elf racial trait: Source
Horror Adventures pg. 39
- Aasimar Alternate Racial Trait: Crusading Magic (+2 Spell Penetration)
- Aasimar Race Trait: Celestial Contact (+1 Caster Level for [good] spells)
- Metamagic Feat: Piercing Spell (+5 Spell Penetration)
- Feat: Spell Specialization (Holy Word) (+2 Caster levels for specific spell)
- Feat: Varisian Tattoo (Evocation) (+1 Caster Level for spells of the specified school)
- Feat: Spell Perfection (Holy Word) (Double bonus caster levels from tattoo and specialization feats)
- Equipment: Orange Prism (Normal) Ioun Stone (+1 Caster Level)
- Equipment: Strand of Prayer Beads(Bead of Karma) (+4 Caster Levels for 10 minutes for Divine Casters)
- Spell: Sure Casting (+5 Spell Penetration for the next spell you cast)
- Divine Obedience: Desna (Starlit Caster), which adds your Charisma modifer to Spell Penetration checks (which is a lot when you are Charisma 40+ in a mythic game)
Forgot to mention the Rod of Metamagic, Piercing as a decent option for a +5 to your penetration checks 3 times per day...