Canon - EF 17-40mm f/4L USM Ultra-Wide Zoom Lens - Black

Yes this will work and shoot with a Canon T Series Cameras. Its an EF-Mount lens so it work on Canons with EF-mounting capabilities. I've used it on a Canon 60D and a Sony a7ii with Metabone Mount. This is a very good lens and a good entry level lens into Photography.

Yes

Yes, will work great with M cameras. You will need the M to EF mount adapter.

Yes, your T6 can use EF lenses. This will fit. However, you will want to research the difference between crop sensors and full frame. The actual focal length on a T6 will be 27-67mm.

Yes. The 30D is APS-C so the lens will function like a 27.2-64mm instead of 17-40mm on a full-frame camera. I used it on my 30D for several years and loved it. Perfect all-around lens at 27-64mm.