You would file a Motion to Disqualify/Recuse Counsel. In it cite the California Rules of Professional Conduct, which you can find at http://www.law.cornell.edu/ethics
/ca/code/CA_CODE.HTM, and specifically Rule 5-210.
However, before you file this you may want to sent him a Notice of Deposition and if he objects, then you file the Motion.
You are going to have to be very, very careful what you ask him and how you ask him because he has an absolute right to assert attorney client privilege on certain matters. You may want to consider hiring a lawyer just to conduct the deposition for you.
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