I think you might be a little confused about this question. The author of the book A Proud Taste of Scarlet and Miniver is E.L. Konigsburg. John Lackland is a character in the book, one of the sons of the main character, the historical figure, Eleanor of Aquitaine.
Perhaps you are looking for quotes by the author about John Lackland. John Lackland was not a very savory or upright character, so the quotes about him are not very flattering. Here are some quotes about him that are found in the book:
"John was...six years old, and he was already a difficult child to like. John had unkind opinions about everything and everyone, and he told them at the top of his voice. John's natural expression was a scowl. John cheated at games, and John told lies".
"There was something unlovely even about his smile; it was so smug that it was challenge not to punch him".
John's brother Henry says of John,
"I wouldn't worry about John...John will find a way to marry and get land. He is already a capable liar and a wonderful cheat. What he cannot gain honesly, he will take without honor" (Part 3, Chapter 4).
Queen Eleanor is quite aware of her son John's character, but her husband is not. She tells King Henry,
"...you've pinned all your hopes on John Lackland. I thought you were a better judge of character than that. Shame on you".
And later she tells him,
"Do you not see what John is? You have allowed me no part in his upbringing, and I cannot see that you have done even an average job. You have seen to it that he has been raised without music; you have formed him of mucus and muscle. He either cries for what he wants, or he punches for it. Snot and sinew! There is no bone there to hang a crown on. I will never, never consent to giving the Aquitaine to John" (Part 3, Chapter 8).