The Collaborative International Dictionary of English v.0.48:

Apposer \Ap*pos"er\, n.
   An examiner; one whose business is to put questions.
   Formerly, in the English Court of Exchequer, an officer who
   audited the sheriffs' accounts.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

APPOSER, Eng. law. An officer of the Court of Exchequer, called the foreign
apposer.