되뇌어 is adjective form of verb 되뇌다
되 is a prefix to mean "repeat"
뇌다 measn "say again"
되뇌다 repeat oneself, remind oneself again by saying it.
Here are some examples) 예시를 들어보면,
잊혀진 사상자들의 이름을 되뇌어 본다
I am repeating over again the name of the forgotten casualties.
되뇌어 생각해보면 말도 안되는 일이야.
If you reconsider it, it doesn't make sense.