Bob is a self-represented plaintiff in a civil case (or, say, private prosecutor in a criminal case). He is also a witness. If the trial is judge-alone aka bench (not jury), he is able to conduct it himself.
At the hearing/trial, Bob (in his capacity as the plaintiff/prosecutor) says:
Your Honour, I call myself.
— and goes to the witness box to be examined by... himself.
Now what? Does he ask himself questions and give answers? Or does he just make statements of fact?
(Any common law jurisdiction)