My GI Dr found a 6mm nodule during my colonoscopy. What could this be?

Depends on pathology. Unless there is a pathologist on site, the polyps undergo a process of fixation, staining, sectioning, and interpretation. Most experienced gastroenterologists can tell you with about 90% accuracy whether a removed polyp/nodule/mass/tumor carries the risk of cancer and whether further intervention is required in the event the polyp may be large or invasive. You should have biopsy results soon.