I was just wondering what is the translation for "いいのにな" in English. I'm kind of confused about that "のに".
It would be helpful if you gave the whole sentence, but you can probably take it as, 'it would good if ... but this is (unfortunately) not the case', which expresses a wish or regret.
For example, おばあちゃんがいるといいのにな
I wish grandma was here.
The な gives the sentence more feeling and makes it sound like the speaker is talking to themselves.