I'm going to guess at this. JB can't be present unless DC is on a witness list and so far isn't on his. So he says he's going to put him on his list so he can be present.
I think AD is the State or District Attorney's office.
An investigative hearing puts DC on the record, but it isn't released under sunshine laws. And I don't think Baez can attend as it stands now.
A deposition is of course the pretrial questioning of a witness, but right now he isn't on anyone's witness list.
Maybe I've just added to the confusion...