How many quarts of oil to fill a 2006 Chevy Trailblazer 6 cylinder?

At least 4.5 quarts. Drain the oil and install a new filter. Start with adding 4.5 and then after starting the engine and running for 1 minute, shut it off, wait 45 minutes and add oil to fill it up if necessary. You will then know the capacity.

It takes 6 quarts of oil per the owners manual.