In December 2027 the son-eomneun days fall on 6, 7, 16, 17, 26, 27. 6 in all. These are days whose lunar date ends in 9 or 0 — long the first thing people check before moving house or opening a shop.
December 25: 기독탄신일; December 27: 대체공휴일(기독탄신일). Taken from Korea Astronomy and Space Science Institute open data.
December 7: 대설; December 22: 동지. Computed from the sun's ecliptic longitude, not looked up in a table.
These dates hold for every visitor. A son-eomneun day is fixed by the lunar calendar alone and has nothing to do with your birth chart. What a given day means for you needs a birth date — there is no auspicious day that holds for everybody.