Are angels all-knowing?

No, they are not omniscient, omnipotent and omnipresent like God, but they have much wisdom.

"But of that day and hour no one knows, not even the angels of heaven, but My Father only" (Matthew 24:36).

"Your maidservant said, 'The word of my lord the king will now be comforting; for as the angel of God, so is my lord the king in discerning good and evil. And may the LORD your God be with you'" (2 Samuel 14:17).

"To bring about this change of affairs your servant Joab has done this thing; but my lord is wise, according to the wisdom of the angel of God, to know everything that is in the earth" (2 Samuel 14:20).