1996 Chevy Blazer emission leak

Well the best way to find it is to connect up a smoke machine and a Tech 2 scan tool and follow the test procedures for the EVAP system. If you don't have those tools handy then post the actual code you have.

There are about 4 parts that cause most of the leaks on these vehicles.
Having the code narrows it down.

The most common one I encounter is the vent solenoid located under the rear of the vehicle above the front of the spare tire. They get sticky and don't close.
The next is a bad fuel cap.
Next on the list is the actual sensor on the fuel pump module.

However without the code and some tests your shooting in the dark.