Would advanced colon cancer show up on a CT scan of my abdomen? Reg CT scan not virtual colonoscopy.

Imaging/biopsy. The imaging modality of ct scan could show findings that would be concerning for cancer, mass around your colon, enlarged lymph nodes in the same area. However, the diagnosis is made at biopsy, a piece of the mass under the microscope of a pathologist. Often the ct scan leads to the biopsy. Good luck, it is important to get the evaluation completed.
Depends. A ct scan does not evaluate colon cancer very well. If there is "advanced" cancer as you asked, possibly a large colon mass could be seen, or if there is metastatic disease to the liver which may also be seen on ct scan. Otherwise, locally advanced cancer contained in the colon or lymph nodes may not be seen on ct scan.
Likely not. On occasion you can see a mass in the colon, but a mass is usually obscured by stool or collapsed bowel.
Not if it's small. Most abdomen ct are routine ct without adequate prep of the bowels. A large mass may be visible on ct but a small one may be obscured by stools. Ct colography is virtual colonoscopy where there is additional colon prep to look for even small colon polyps.