In this page you can find all secrets in Uncharted: Lost Legacy that can be unlocked in the prologue. This mission has only two secrets and you can get them without any problems.
Warning - The secrets are described in suggested way of unlocking them.
You can take this photo when you are going through the marketplace. Look for a small white circle that changes into a camera icon when you get closer to it. This place is presented in the picture above.
Treasure 1/1 -Ganesh Figurine
You can't miss the moment of getting this treasure because, in default, the figurine belongs to Chloe. The game allows you to take this artifact after Meenu steals it from Chloe during your walk through the marketplace.