John Gill Commentary 2 Samuel 7:20

"And what can David say more unto thee? for thou knowest thy servant, O Lord Jehovah." — 2 Samuel 7:20 (ASV)

And what can David say more to you
In a way of self-abasement, or in thankfulness for such wonderful favours, or in prayer for more and other mercies; he wants words, as if he should say, to express his sense of your own nothingness and unworthiness, and to praise the Lord for all your benefits; and so large are the grants and promises made, that there is no room for him to ask for more:

for you, Lord God, know your servant ;
what a sense he has of his own meanness and vileness, what gratitude his heart is filled with, and what your wants and your necessities are, which God only can supply, and does abundantly, even more than he is able to ask or think. The Targum is, ``and you have performed the petition of your servant, O Lord God.''