과감하다 means "drastic, daring, decisive, bold"
ex)
그 여배우는 과감하게 파인 옷을 즐겨 입는다
The actress enjoys wearing daring clothes.
그는 좀 더 과감해지기로 결심했다
He decided to take the bull by the horns.
당돌하다
- daring, plucky, (informal) spunky
ex)
그는 매우 당돌하다
He is plucky.
그 아이는 질문에 당돌하게 대답했다
The child gave a spunky reply to the question.
- rude, insolent
ex)
그는 선생님에게 당돌하게 굴었다
He was insolent to the teacher.
어른 앞에서 그렇게 말하다니 참 당돌하다
It is very rude of you to talk like that to your elders.
과감하다 and 당돌하다 both can mean "daring"
과감하다 has a nuance of "bold"
당돌하다 has a nuance of "rude"
You should use 당돌하다 to a person younger than you.