소견서가 · 소견서를
doctor's note, medical opinion letter, referral
Example
큰 병원에 가려면 동네 병원에서 소견서를 받아 오세요.
To go to a big hospital, get a referral letter from your local clinic.
Word parts
소 that which+견 see+서 document
Literally 'document of what was seen'; -서 = written document: 신청서, 계약서.
Good to know
진단서 officially certifies a diagnosis; 소견서 is the doctor's opinion, often used for referrals.