This is something that’s troubled me also to some degree. Though I’ve not encountered the extreme version you have encountered, except in learning about “Jehovah’s Witnesses.”
Jason Evert’s book “Answering Jehovah’s Witnesses” says in regard to the ever present question of Matthew 24:36 and Mark 13:32 (no man knows the day or hour when heaven and earth will pass away, not even angels or the Son, but the Father alone knows). That was a summary, not a quote. I think those verses are what people eventually latch on to, if they can hold to nothing else. It’s what comes to my mind at least.
Evert says basically on p. 85 that other portions of Scripture, such as John 16:30 and 21:17 make it clear that Jesus does know everything… one must necessarily make a distinction between Christ’s human nature and divine nature. When Jesus seemingly doesn’t know something, it is because He is speaking from His limited human nature; contrarily, when He “knows everything,” He is speaking from His divine nature.
I’m not sure if that is a completely satisfactory answer. I thought it kind of odd myself. But taken in line with the CCC 474, it makes pretty good sense. Evert’s opinion is not necessarily that of the Magesterium though.
Also, you may check out St. Augustine’s major work on the Trinity. I think he addresses it in Book 1. Just read it all though
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St. Augustine ranks higher than Jason Evert (no offense to Evert, I learned a lot from his book) on the “scale” of Catholic authority. I’m sure Jason would agree with me on that, knowing I imply only good to him, but more good to Augustine
(I Corinthians 15:41).