A *** 16 card.

"A says I can't guess", so it can't be those numbers that don't repeat 2.4.9.j.k

"B said I knew you'd say the same thing", so the color is definitely not a plum blossom with no repeated numbers.

Now there are only spades: A 7 Q and diamonds: A 5.

"A says I guess now", so the number A knows is definitely not A.

Now there are only spades: 7 Q and diamonds: 5.

"B said I guessed it, too." So the suit that B knows is definitely not spades with two cards left.

So it is a square 5.