Please help me on a road of reasoning.

Mr. p knows the number of points, but he doesn't know the color. If he doesn't know what this card is, it means there is more than one card with this number.

Mr. Q knows the suit of this card, so it can be inferred that Mr. P certainly doesn't know this card, which means that every card of this suit has a card with the same number of points but different suits. So the suit of this card is either hearts or diamonds.

Because only spades and flowers are counted in 16 cards, Mr. P can infer that this card is not spades and flowers by Mr. Q not knowing what card he is.

Mr. P knows what card he is, that is to say, if Mr. P has a red heart in his hand, there must be no cards in the square with the same number of points as him (because it is definitely not spades and flowers). Similarly, if this card is a square, then there must be no cards with the same number of points in mind. So we can infer that this card is one of the three cards of hearts Q, 4 or diamonds 5.

Mr. Q can know what this card is through Mr. P. It can be seen that after excluding the unqualified cards in this suit, there must be only one card left. If it is a heart, then there are two cards that meet the requirements, so Mr. Q can't infer that it can only be a square, and we have dealt an A in front of it, so this card is a square 5.