The only easily done maintenances for a manual or automatic transmission is the Transmission Fluid change. While Chevy says that this should be done every 100,000 miles, I did mine at 50,000 with royal purple and the transmission has been fantastic since then. I am currently at 85,000 with an original clutch and transmission.
With a 07 chevy cobalt key
It is bolted in the valve body that is inside of the transmission.
The shift solenoid on a 2007 Chevy Cobalt is located inside the transmission. Specifically, it is typically found on the valve body or the transmission control module. Accessing it usually requires removing the transmission pan and may involve displacing some components, so it's advisable to consult a repair manual or a professional mechanic for detailed guidance.
in the trunk
It does not have one.
No it will not
87 octane
.040
to the low side
13.3
100lbs
see your Chevy parts man.