Can multiclass spellcasters combine their levels to satisfy
the level prerequisites for item creation feats? For example,
the Forge Ring feat requires a spellcaster of level 12+. If I
am a 6th-level cleric/6th-level wizard do I qualify, or would
I need to be 12th level in one or the other?
  You need to have the listed number of levels in a single
spellcasting class. In the case of Forge Ring, you need 12 levels
in a spellcasting class. Note that if you have a prestige class
that improves the spellcasting ability of another class, you use
your effective caster level to meet the prerequisite. For
example, a 10th-level wizard/2nd-level loremaster is a 12th-
level spellcaster and meets the prerequisite for Forge Ring.