As above, depends on the county. In Nashville (Davidson and surrounding counties) they plug into your computer and visually inspect for a catalytic convertor and do a sniff test on exhaust. In Memphis (Shelby county) they test all systems (lights, wipers, parking brake, exhaust sniff).
I think the only counties that require emissions testing are Davidson, Shelby, Hamilton, Rutherford, Sumner, Williamson, and Wilson counties.
Check:
The Official State of Tennessee's Department of Environment and Conservation, State Parks Website
TN is now sponsoring a "Smoke School"--no joke, check their website. So we may see a visible smoke test on our diesels in the near future--I think California does this.
Just call your local courthouse if you can't find it on the internet and ask what is required to get your tags---if they says emissions pass, then have fun...
Good thing is, many counties in TN do not require testing.
Also, you don't show the year of your truck---that will tell a lot about what you are facing...