Sonja, that's a really cool coin!
These were minted in copper only in 1838. What looks like a large stylized 'R' on the front is actually the monogram of Frederik VI, King of Denmark from 1808 to 1839. These coins were minted during the end of his reign, and remain scarce in better grades.
The inscription 'RB SK' stands for 'rigsbankskilling'. The 'rigsbank' was the national bank of Denmark at the time, and 'skilling' is an etymological cognate of the English word 'shilling'.
The catalogs are good to these coins, reporting pleasing values:
worn: $8 US dollars approximate catalog value
average circulated: $35
well preserved (as in our picture): $60
fully uncirculated: $110
The coin in our image comes from eBay seller Foothils Coins and Stamps. It is a nice specimen. It has slight wear, a light and even toning, and no major problems. It was being sold for $40 USD, but went for an unknown best offer.
If you were to sell a similar coin to a dealer, expect between $15 and $25 dollars. This mark-up is required to keep a dealership afloat.