Imperial player activates a storm trooper group.

All 3 figures are in LOS of jyn.

Does she get to quick draw and attack all 3 figures or 1 figure out of the 3.

I'd argue the later based on wording of the ability and wording of activation but seeking clarification.

You may use Quick Draw at the start of a FIGURE's activation - so a single figure. Not a deployment group.

Quick Draw can only be used against a single hostile figure.

"Activation Phase", RRG, Page 3:

While activating a group of two or more figures, the player activates all figures in the group, one at a time , in the order of his choice.