In principal, without any exemption, the dormitory requires a Chest X-Ray when checking-in.
Even if you took a skin test, it is not replaced with the chest X-ray.
In case it's impossible to take a chest X-ray in your country, please take a test of Chest X-Ray after your arrival to Korea which takes less than 30 minutes.
Please feel free to refer to the information of hospital around the dorms, where you can take a Chest X-Ray.
https://dorm.skku.edu/dorm_seoul_eng/notice/notice_english.jsp?mode=view&article_no=64160&board_wrapper=%2Fdorm_seoul_eng%2Fnotice%2Fnotice_english.jsp&pager.offset=0&board_no=78&default:category_id=103&no=153