The Catholic Truth Society (who are the official publishers to the Holy See in Rome) appear to offer no answer to the excellent question they ask themselves in the tweet below: How could Jesus, as God, pray to God?
Read the article they link to here
The CTS article concludes:
This reading of the Trinity may not answer how Jesus prayed to himself in a ‘textbook answer’ way, but it does reveal the importance of that question. Not only is Jesus giving us an example of how to pray to the Father, but he is also revealing the importance of seeing God as a relationship.
So the Catholic Church seems to have given up attempting to explain why on earth Jesus who is allegedly God would bother praying to himself. Was Jesus just play-acting for his disciples?
When, according to the gospels, he fell with his face to the ground and prayed, “My Father, if it is possible, may this cup be taken from me. Yet not as I will, but as you will” was he really praying to himself? Also, does the Father pray to Jesus? Does the Holy Spirit pray to Jesus too?