This achievement takes place in The Showstopper mission in Paris. You have to pose as Tobias Reaper and sneak into the secret auction held on the third floor. The path is simple with little to no risk of detection.
Walk in through the main doors and head for the doors to the right of the large staircase. Follow the hallway to the right until you come out onto a busy patio. Continue around to the back of the building and look for a pipe wedged in the corner. Climb up to the third floor balcony and head back inside. Across the hall from where you entered, you'll see two white and gold doors. Enter that room, sit in an empty chair and wait for Margolis to finish her speech. After a short conversation, the achievement will pop.
If you have any questions, please let me know!