**Core Concept**
The diagnosis of colonic diverticulosis involves identifying the presence of diverticula, which are small, bulging pouches in the digestive tract, most commonly in the colon. **Colonic diverticulosis** is a condition where these diverticula are present without symptoms or complications. The best investigation should accurately visualize the colon to detect these pouches.

**Why the Correct Answer is Right**
Since the options are not provided, a general approach to diagnosing colonic diverticulosis is through imaging studies that can clearly show the structure of the colon. **Colonoscopy** is often considered the gold standard for detecting diverticula because it allows direct visualization of the inner lining of the colon. However, other imaging techniques like **CT colonography** can also be effective in identifying diverticula, especially in patients who cannot undergo colonoscopy.

**Why Each Wrong Option is Incorrect**
Without specific options, it's challenging to address each directly. Generally, options that do not involve direct or indirect visualization of the colon (like certain blood tests or non-specific X-rays) would be incorrect because they cannot accurately diagnose diverticulosis.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that while **diverticulosis** refers to the presence of diverticula without symptoms, **diverticulitis** occurs when these diverticula become inflamed, which can lead to more severe symptoms and complications. Accurate diagnosis is crucial for appropriate management.

**Correct Answer:** D. Colonoscopy