It’s interesting to think about how Jonah views himself in the bodies he takes.

Like, does he view Elias, James, Richard, etc. just as vessels and masks while his conciousness is the only thing that is him?

Or does he become Elias? How does he refer to himself in his own head? 

He’s so used to referring to himself in the third person (“Jonah Magnus did [x]. He was [x].”), does it take him a moment to recognize that someone is referring to him when they call him by his name (does anyone call him by his name anymore)?

How has his perception of self changed over the years? Does he have a true perception of self anymore?

Okay, so, based on the quote from MAG 158 'Exactly where they’ve always been, Martin. Watching over my Institute.' I kinda head cannon that Jonah sees himself at this point as separate from even his own original body, seeing it as nothing but an old vessel for his eyes and maybe one of the things keeping him alive. So his consciousness might very well be the only thing that is truly him.

That said, I think he would probably refer to himself with the name of whoever he is currently inhabiting, but might throw in the occasional Jonah when he is sure that there is no one around that might catch him for even a moment off guard.