Speak to Procter Quinlan and select the option to assist on a patrol. This is basically an escort mission. You have to protect the scribe as she collects data. The scribe is located on the airport. Talk to him/her and travel to the location he/she’ll mark in the map. Once there, kill all enemies and protect the scribe as he/she retrieves the data. When done, return to the Prydwen and report to Procter Quinlan.
Tip: This quest is one way to "farm" experience. Even if the scribe is killed, you'll still get experience by returning to Proctor Quinlan so it's possible for you to let him/her die in the hands of enemies or murder him/her yourself.