all clinicians:

SELECT r.*
FROM referrer r
  JOIN referrer_posting rp
    ON r.id = rp.referrer_id
  JOIN hospital h
    ON h.location_id = rp.location_id

WHERE h.region_code = 'RR8'

SELECT r.*
FROM referrer r
  JOIN clinician_region cr
    ON cr.referrer_id = r.id
WHERE
  cr.region_code = 'RR8'