When they do a colon scope can they see if c diff is or was present?

Yes and no: Clostridium difficile may be present but not causing illness, and if so, it is moot and will not be visible on colonoscopy. The pseudomembranous colitis that is often caused by c difficile is obvious on colonoscopy.

Sometimes...: C. Difficile, when pathologic, is a bacterial infection that may be accompanied by colonoscopically visible signs of colitis which then warrants specialized antibiotic treatment ; needs documentation of eradication. Often c.Difficile causes only mild irrigation of the colon lining, or no readily appreciable mucosal changes unless biopsies are taken. Sometimes, only stool analysis is diagnostic.