23.  The Board may require all or any of such trustees and persons as aforesaid to attend before it respectively at such times and places as are reasonably appointed, for the purpose of being examined in relation to the endowment, and to answer the questions put to them, and to produce upon their examination any documents in their custody or power relating to the endowment or the property thereof, and may examine upon oath or otherwise all such persons and all persons voluntarily attending and may administer oaths.