Final answer:
Phoneme-specific nasal emissions are best determined using nasometry or nasopharyngoscopy, which provide specific insights into nasal airflow and the visual evaluation of the nasopharynx during speech, respectively.
Step-by-step explanation:
Phoneme-specific nasal emissions can be detected using a variety of diagnostic techniques, one of which is nasometry. This technique measures the acoustic correlates of nasal airflow and can help determine if there is abnormal nasal sound during speech, which might be indicative of velopharyngeal insufficiency or other related conditions. Other potential methods mentioned, such as spirometry and nebulizers, are primarily used to assess lung function and are not the most appropriate for assessing the phoneme-specific nasal emissions. For a definitive evaluation of the velopharyngeal mechanism during speech, nasopharyngoscopy can be employed. This involves the use of a small, flexible endoscope to visually examine the nasal passages, velum, and the area of the nasopharynx during speech and is quite effective for this purpose.