Fine! Let Mr.Muller submit them in writing. "a written question that is formally put to one party in a case by another party and that must be answered." That is called an interrogatory. President Trump doesn't have to physically be there - as a matter of fact....POTUS must NOT speak to Mr. Muller....a snake that will bite him for sure!!
perhaps the list was in Cohens office?
the Times report said Trump’s lawyers compiled the questions into a list and that document was “provided to The Times by a person outside Mr. Trump’s legal team.”
http://hosted.ap.org/dynamic/stories/U/US_TRUMP_RUSSIA_PROBE?SITE=TXMCA&SECTION=HOME&TEMPLATE=DEFAULT&CTIME=2018-05-01-08-41-10