Awwwww…..a cool, old, side lever hammer drilling with a dolls head extension!!! I do love hammer drillings. A question before I tell you what I see. Is there a name in a banner on the rib? As you did not mention a name, I assume not? No biggy, there is lots of unmarked, pre-WWI and pre-WWII German firearms floating around. I have a couple.
Dat of manufacture is before 1920 I believe. I would guess between 1900 and immediately after WWI. Those proofs are largely from the 1891-93 proof law. I can never remember which proof house, Suhl or Zella-Mehlis stamped the bore diameter "118/35". That SHOULD be the 9.3 X 72R cartridge but to be certain a chamber cast should be made as well as slugging the bore. One thing to be aware of; though 9.3 is .366 caliber a great many 9.3 X 72R rifles are tightly bored and are more than happy with.358 bullets. That's just another reason to slug the bore and make a chamber cast.
On the rifle barrel, the crown over "G" simply denotes a rifled barrel. The crown over "U" stands for a thorough visual examination. If that is a script "K" in the circle on the rifle barrel, it MIGHT be that the barrels were made by one of the many Kelber gunsmiths.
Shotgun barrels, the crown over "U" is the same. Crown over "S" denotes a shotgun barrel and the crown over "W" means it is a choked barrel but, the amount of choke will have to be measured. The right barrel is probably cylinder bore. The circled 16 is as Marblekonus mentioned, 16 bore with 2 1/2 in. chambers.
I don't see a crown over "N" which would denote Nitro Proof, (smokeless powder). So, unless there is some indication on Nitro proofing, you have a drilling that is only proofed for black powder.
I can't quite make out what is in front of "FLUSSTAHL" but that means 'fluid steel' and the word in front of it is more than likely the maker of the barrel steel.
Value....there's a spread, obviously. Bore condition is important and you didn't mention any of them. Without seeing the gun personally, from $1200 to $1800 and that's just one man's opinion.