Yesterday I came back from a fair in Ohio, which was selling assorted weapons. I had bought a dagger, but I'm a bit curious if I can even own one, and if there's any specific laws for it. I have no plans to carry/use it, and it is mostly for show. Help?
To answer you question in very brief terms: You can own one and keep it at home, but not carry it. This falls under the "curio" exception to law. Besides, it's not like cops are going to storm your house looking for knives out of the blue, and even if they did, you are already in much bigger trouble.
The only way carry would be legal is if this "dagger" is actually a known tool of some sort with a non-weapon use and is carried with that use in mind. For example, "duct knives" sold at hardware stores are doubled-edged daggers, but are used for HVAC installation. Some chisels are double-edged, as are some leatherworking tools.
Is it designed for combat and "serves no common lawful purpose"? Then it's illegal to carry. If it has a purpose other than combat, then it's legal. There is absolutely no hard "yes" or "no" I can give you because of this vagueness in PA law. However, to date I have never seen a conviction in the courts for a normal manually operated folding knife except for one that orients into a punch-dagger.