In the editor just click to add a C++ class. Call it Structs or something. Then put your structs and enums in it. Other C++ files just #include the header and they can use enums or structs in it. The game will have it. I have a file full of static blueprint callable functions that I also have some of my enums in, for more global type enums. If only one class is using them I put them in the header with the class.