Finding the best temperature to print with a specific spool of filament is as simple as printing three different sample versions.
In this example I printed a simple cup (in PETG, 1mm nozzle, spiral mode) at 240 degrees. It came out a bit rough. Then I printed a second version, at 10 degrees higher (250), thinking that a higher temperature might smooth out the bumps, but the bumps got bumpier instead. Then I printed a third version, at 5 degrees lower (235), and the print got prettier, with no bumps.
The default temperature for a material will not necessarily give the best results. You need to find your own!