I heard that..., They said that..., Recalling what was said
This expression is a combination of -는다고 하다, indicating a citation, and -던데, indicating recollection. It is used when recalling or confirming something you heard somebody else say previously. Thus, the correct form of this expression also depends on the sentence type of what was heard previously. The clause that follows this expression can indicate the speaker’s opinion, question, advice or invitation with respect to the topic under discussion.
For adjectives in the present tense, both -냐고 하던데 and -으냐고 하던데 are acceptable, while for verbs in the present tense, both -냐고 하던데 and -느냐고 하던데 are acceptable.
1. The -고 하- of this expression can be omitted.
2. This expression can also come at the end of a sentence. In this position, while still expressing something that the speaker heard previously, it also indicates either the speaker's disagreement with the other person's opinion or the speaker's expectation of a response from the other person.