School Understanding wrote:
School Understanding: The arcanist can select one arcane school from any of the schools available to a character with the arcane school wizard class feature, but does not have to select any opposition schools. The arcanist gains one ability of that arcane school as though she were a 1st-level wizard, using her Charisma modifier in place of her Intelligence modifier for this ability. The ability must be one gained at 1st level and is limited in its use per day to 3 + the arcanist's Charisma modifier. As a swift action, the arcanist can expend 1 point from her arcane reservoir to bolster her understanding, allowing her to treat her arcanist level as her wizard level for the purpose of using this ability for a number of rounds equal to her Charisma modifier (minimum 1). During this time, she also gains use of the other ability gained at 1st level for her selected school. She does not gain any other abilities when using this exploit in this way, such as those gained at 8th level.
I think it's pretty clear. You use Reveal Weakness as if you were a level 1 wizard, and a level 1 wizard would have caster level 1.