knee
at your mother's (or father's) knee at an early age.
the bee's knees: seebee.
bow (or bend) the knee: seebow.
bring someone or something to their knees reduce someone or something to a state of weakness or submission.
2013CNN transcripts The fall of Lehman Brothers nearly brought several of the world's financial institutions to their knees.
on bended knee: seebended.
on your knees
1 in a kneeling position.
2 on the verge of collapse.
weak at the knees overcome by a strong emotion.
your knees are knocking you are feeling very frightened. informal