**Core Concept**
The clinical presentation described is suggestive of a scalp infection, likely a form of hidradenitis suppurativa or a scalp abscess. However, the presence of easily pluckable hair and boggy swelling with discharging sinuses, along with cervical lymphadenopathy, points towards a specific diagnosis. This condition requires further investigation to confirm the underlying cause.

**Why the Correct Answer is Right**
The correct approach to diagnosis involves a combination of clinical examination, imaging studies, and histopathological examination. In this case, a scalp biopsy would be the most informative diagnostic test. This would allow for the examination of the scalp tissue under a microscope to identify the underlying cause of the infection, such as a fungal or bacterial infection, or a condition like tinea capitis.

**Why Each Wrong Option is Incorrect**
**Option A:** A routine blood culture would not be the initial diagnostic step in this case, as it may not provide specific information about the infection affecting the scalp.

**Option B:** A CT scan of the scalp may provide some information about the extent of the infection, but it would not be the primary diagnostic tool for identifying the underlying cause.

**Option C:** A skin scraping examination may be useful in identifying fungal infections, but it may not be sufficient for diagnosing other conditions that could be causing the symptoms described.

**Option D:** A scalp swab culture may provide some information about the bacterial flora present, but it would not be the most informative diagnostic test in this case.

**Clinical Pearl / High-Yield Fact**
In cases of scalp infections, it's essential to consider the possibility of a fungal infection, particularly tinea capitis, which can be diagnosed with a scalp biopsy and treated with antifungal medications.

**Correct Answer:** C.