다는 것 같다

it seems they said that ~

-다는 packs a reported statement into a modifier and 것 같다 hedges it, so the speaker is passing on something they heard while flagging that they are not sure of it: 아 친구가 내려갔다는 것 같은데? (I think she said her friend went down). Compare plain -는 것 같다, which guesses from what you can see; -다는 것 같다 guesses about what was said.

Register: neutral, cautious