The XP points for the PCs depends on the LVL of the PCs and the CL of the encounter. In The Traitor's Gambit the guide itself tells you when to give the XP and how much.
If you need help to estimate the XP you can check on the Core Rulebook page 248.
If you want help to measure encounter difficulty just go back to page 247.
Here on The Saga Continues they created a MUST HAVE SAGA Index where, in addiction of other things, you can find a CL Calculator.
If you want some clarification about the exact time the PCs levels up during the missions, moving from LVL 1 to LVL 3, I can only talk from my little experience as GM and by the istructions provided at page 2 of the PDF:
This first adventure will get the heroes together and launch them down
a path to making a big difference in the galaxy, and the heroes should
advance to 3rd level by the conclusion of the adventure.
So, presuming they start with LVL 1 PCs, they should advance to LVL 3 at least by the end of the last part of The Traitor's Gambit: Imperial Prison Facility