From Longman Dictionary of Contemporary Englishon your kneeson your kneesREGRET/FEEL SORRYin a way that shows you have no power but want or need something very much He went on his knees begging for his job back. → knee
Examples from the Corpus
on your knees• McAllister should be on his knees after a gruelling month at Elland Road.• Pausing outside his living room door, he switched on the hall light and crouched down on his knees.• When I saw him a week later he got down on his knees and asked me to forgive him what he done.• Painfully she wallows down on her knees and without diffidence soaps and rinses me all over.• He gave no trouble and sat with his head down and his elbows on his knees, hands loose and empty.• You know the lasting image: Hendrix on his knees, summoning fire from a flaming Stratocaster guitar.• Pearl had sat straight in her chair; her hands overturned on her knees.• But now the Captain was on his knees beside the coffin praying. 