how to install a spark plug boot on a 2006 Cadillac cts engine 3.6 v-6

What do you mean by boot? The 3.6 does not have a boot. It has a coil, and spark plug. Which cylinder as well, there are only two cylinders that can be serviced without upper intake removal.

Thanks for the reply. How can you tell which coil is arching? I can hear the spark jumping but no visual in the dark.

You will probably have no visual, as the spark is delivered at the bottom of the port at the plug. From a shadetree standpoint, if it is continuously misfiring, you could try and disconnect each coil, 1 at a time. Is the check engine light on?, it should be. A diagnostic test may point to a single cylinder by code, or in misfire data.