So confused on the timing rules here. Nym has Genius equipped with Trajectory Sim. Nym does a Talon Roll, end of the Manuver should be assigned a stress. Yet he uses trajectory Simulator from Genius ability? I thought the Stress from the Talon Roll would prevent the free action from Genius ergo no bomb use?

Genius isn't an action, free or otherwise, so stress has no impact on its activation.

FAQ v4.4.0 (effective as of 11-06-2017) Errata card for reference:

All you need to do is reveal and execute a maneuver while having a bomb upgrade card (without the " A CTION :" header) available to discard and drop the corresponding token. When you go to drop the token you may use Trajectory Simulator to launch the bomb instead of dropping it.

Fun mathematics: a bomb launched in this way from a Scurrg (3-speed t-roll) will land ~2.8 base widths to the left/right of where a normally dropped bomb would've landed if you t-roll as far back as possible.