Query Error: Error: ER_NON_UNIQ_ERROR: Column 'candidate_id' in field list is ambiguous
Your query is right, only

    SELECT user_name, can.candidate_id
FROM user AS usr INNER JOIN candidate as can
ON usr.user_id = can.entered_by
INNER JOIN candidate_joborder as canjo
ON can.candidate_id = canjo.candidate_id
WHERE usr.user_id = 1