I got a miscellaneous objective that's called Talk to Bobbi. When I go up to the door it says I need a key. She supposed to come up to the door and open the little door window to talk to me. How can I solve this?

Hmm, might be bugged. I would save the game outside of Goodneighbor. Close Fallout 4 then restart it and go back into Goodneighbor and see if she talks to you then.

Bring flowers maybe arrange a date I dunno.

But how will she smell them if she has no nose?

Myth busted.

Did you try at night?