Where is model number on Stevens shotgun Patented August 12 1913 single barrel ser KT988 12 gauge?

The model number on a Stevens shotgun, particularly the single barrel models, is typically located on the barrel or the frame. In your case, it may be stamped on the left side of the barrel or on the receiver near the trigger guard. Additionally, you can check the underside of the barrel, as some markings can be found there. If you have difficulty locating it, consult a detailed guide or reference for Stevens shotguns from that era.