This coin comes from the German State of Saxony after the states congealed into the German Empire in 1871. The 10 mark coin contains 0.1152 troy ounces of gold. The 20 mark coin looks the same, but it is bigger and contains 0.2304 ounces of gold. At more than $1400 US dollars per ounce current gold value, the base value (BV) of the 10 mark coin is more than 0.1152 x $1400 = about $160, and double that for the 20 mark.
$1400 per ounce was the price of gold when this article was written. Today it is different. Use a web site such as kitco.com to find the current price of gold. It changes every day.
Added value, over and above the base value computed above, is due to collector appeal and is proportional to the condition of your coin. The coin in the picture has a fair amount of wear, which we call 'average circulated:
VALUE OF SAXONY 10 AND 20 MARKS (all dates):
worn: base value (BV) of gold content
average circulated: BV + $100
well preserved: BV + $200
fully uncirculated: BV + $400
The reason I say the coin in the picture has wear is because its luster is gone. A fully uncirculated lustrous coin looks almost creamy or satiny, not shiney. The luster comes from tiny striations in the surface which radiate outward from the center of the coin. They are imparted to the coin during the striking process. An experienced numismatist can spot genuine luster in a heartbeat. Sometimes luster is 'added' to a coin using steel wool or similar abrasive. This is called 'whizzing' and immediately renders the coin valueless to experienced collectors.
A dealer would pay about the base value of the gold plus about one-half of the added collector value.
A coin with problems, such as a coin that has been holed to be worn in a pendant, or a coin with heavy wear and staining, will only be worth the base gold value of the coin.
NEVER CLEAN A COIN. CLEANING RUINS VALUE.
One of my favorite web sites for old German coins is MA Shops. Look around that site for coins like yours.