Does anybody know if I would be able to fit a 29 inch tire and if so how wide on a Trek Utopia Dual Sport?
Depending on tread design...
The widest with the stock front derailer you can go is 29x2.0. The recommended tire to use with this set up is a Bontrager 29-3(rear specific) tire.
You can, however go even WIDER tire(29x2.1-29x2.25) if you replace the Front Derailer with a Shimano SLX derailer. See pic. LOTS of CLEARANCE.