According to Endoscopic surgeon Dr. Tapan Shah, Gastroscopy is an Endoscopy which is done to see any disease or lesion in the esophagus, stomach, and duodenum.
For that symptoms are frequent upper abdominal pain, acidity, nausea, and vomiting.
Colonoscopy is an Endoscopy which is done to see whole large intestine and last part of the small intestine.
Symptoms are bleeding per rectum or chronic constipation, diarrhea. So a doctor can check it.