Baseboard socket plug replacement
This appears to be an ancient Edison-screw-receptacle

What you have appears to be an ancient sort of receptacle, from the days when people put Edison screw bases on the end of cords because standard NEMA receptacles weren't a thing yet.  I'd put a new single-gang old work box in there with the correct tubing/bushings for that old K&amp;T wiring, and then fit a 15A GFCI receptacle at that location; just be careful to make sure you don't get hot and neutral mixed up!