Is there a specifc order in which these are used? I am curious what happens if I attack with Trenloe, then the dodgin enemy chooses to dodge, can I then use his reroll to reroll one of the dice agan? What about aim v dodge?

Aim vs. Dodge cancels it out (i.e. if someone dodges an aimed attack, there are no rerolls). Trenloe and a few other reroll-certain-dice abilities there's nothing specific stated on a dodge. In our games, we've had the attacker do all the rerolls he chooses, then the defender chooses the ones he wants.

-shnar

"Trenloe cannot use this ability if he is aiming or if his target is dodging." Pretty clear-cut.

As shnar said, if an attack is both aimed and dodged, the effects cancel and no reroll takes place. This is on page 14 of the rules (under Dodge) and again on page 17 (under Re-rolls).