Dante says "I" a lot, which gives us a clue. And we frequently see the inner workings of his thoughts. But this first person POV (point of view) goes through a twist in Paradiso that does not exist in Inferno or Purgatorio. In the first two cantiche, we pretty much trusted everything Dante said without a doubt. But that attitude hits some snags here in Heaven because even Dante can't trust what he's saying. Because so much of what he sees is beyond the scope of human language, he has to make do with imperfect tools to describe an infinitely perfect realm. However, we readers have no clue what Heaven is like either and we're just as human as Dante. So we must eventually put our faith in him and imagine what he's describing the best we can.
Another interesting thing author-Dante does with this point of view is that he often hides character-Dante's doubts and questions. We have no idea what bone Dante is picking, until some other character swoops in, plucks that thought from Dante's mind, and lays it out for us. That's the advantage to having psychic characters. But it also means that character-Dante has no privacy. Every single thought – from his awe to his adoration to hidden doubts and moments of weakness – is visible for us to see. When Dante's pride flares up, Beatrice sees it and smashes it. Similarly, St. John calls Dante out for giving insufficient answers (in the test of charity) when he knows Dante has the knowledge to do better. Not an easy thing to live with, but it's all part of showing Dante how to make his will conform to God's.